The only difference between this problem and D1 is that you don't have to provide the way to construct the answer in D1, but you have to do it in this problem.

There's a table of n × m cells (n rows and m columns). The value of n ⋅ m is even.

A domino is a figure that consists of two cells having a common side. It may be horizontal (one of the cells is to the right of the other) or vertical (one of the cells is above the other).

You need to place nm/2 dominoes on the table so that exactly k of them are horizontal and all the other dominoes are vertical. The dominoes cannot overlap and must fill the whole table.

Input

The first line contains one integer t (1 ≤ t ≤ 10) — the number of test cases. Then t test cases follow.

Each test case consists of a single line. The line contains three integers n, m, k (1 ≤ n,m ≤ 100, 0 ≤ k ≤ nm/2, n ⋅ m is even) — the count of rows, columns and horizontal dominoes, respectively.

Output

For each test case:

  * print "NO" if it's not possible to place the dominoes on the table in the described way; 
  * otherwise, print "YES" on a separate line, then print n lines so that each of them contains m lowercase letters of the Latin alphabet — the layout of the dominoes on the table. Each cell of the table must be marked by the letter so that for every two cells having a common side, they are marked by the same letters if and only if they are occupied by the same domino. I.e. both cells of the same domino must be marked with the same letter, but two dominoes that share a side must be marked with different letters. If there are multiple solutions, print any of them. 

Example

Input


8
4 4 2
2 3 0
3 2 3
1 2 0
2 4 2
5 2 2
2 17 16
2 1 1


Output


YES
accx
aegx
bega
bdda
YES
aha
aha
YES
zz
aa
zz
NO
YES
aaza
bbza
NO
YES
bbaabbaabbaabbaay
ddccddccddccddccy
NO

Source: codeforces | Difficulty: HARD
Tags: Mathematics

Implementation

Constructive algorithms


Solutions:
import io
import os
import collections
import math
import functools
import itertools
import bisect
import heapq
from sys import stdin, stdout, stderr
from collections import *
from math import *
from functools import *
from itertools import *
from heapq import *
from bisect import bisect_left, bisect_right, insort_left, insort_right
input = io.BytesIO(os.read(0, os.fstat(0).st_size)).readline

def get_ints():
	return list(map(int, input().split()))

def get_int():
	return int(input())

def get_str():
	return ''.join(list(map(chr, input()))[:-1])

def eprint(*args):
	stderr.write(', '.join(map(str, args)) + '\n')

def print(*args):
	stdout.write(' '.join(map(str, args)) + '\n')
t = get_int()
for tt in range(t):
	(n, m, hor) = get_ints()
	total = n * m // 2
	vert = total - hor
	h_forced = v_forced = 0
	both = n // 2 * 2 * (m // 2 * 2) // 2
	if n % 2 == 1:
		h_forced = m // 2
	elif m % 2 == 1:
		v_forced = n // 2
	if h_forced > hor or v_forced > vert:
		print('NO')
		continue
	hor -= h_forced
	vert -= v_forced
	if hor % 2 == 1 or vert % 2 == 1:
		print('NO')
		continue
	print('YES')
	grid = [['a'] * m for _ in range(n)]
	if n % 2 == 1:
		char = 'x'
		for x in range(0, m, 2):
			grid[-1][x] = grid[-1][x + 1] = char
			if char == 'x':
				char = 'y'
			else:
				char = 'x'
	if m % 2 == 1:
		char = 'x'
		for y in range(0, n, 2):
			grid[y][-1] = grid[y + 1][-1] = char
			if char == 'x':
				char = 'y'
			else:
				char = 'x'
	hchars = ['q', 'w', 'e', 'r', 't', 'z', 'u', 'i']
	vchars = ['a', 's', 'd', 'f', 'g', 'h', 'j', 'k']
	ci = 0
	for y in range(n // 2):
		for x in range(m // 2):
			if hor:
				if y % 2 == 0 and x % 2 == 0:
					(c1, c2) = (hchars[0], hchars[1])
				elif y % 2 == 1 and x % 2 == 0:
					(c1, c2) = (hchars[2], hchars[3])
				elif y % 2 == 0 and x % 2 == 1:
					(c1, c2) = (hchars[4], hchars[5])
				elif y % 2 == 1 and x % 2 == 1:
					(c1, c2) = (hchars[6], hchars[7])
				grid[2 * y][2 * x] = grid[2 * y][2 * x + 1] = c1
				grid[2 * y + 1][2 * x] = grid[2 * y + 1][2 * x + 1] = c2
				hor -= 2
			else:
				if y % 2 == 0 and x % 2 == 0:
					(c1, c2) = (vchars[0], vchars[1])
				elif y % 2 == 1 and x % 2 == 0:
					(c1, c2) = (vchars[2], vchars[3])
				elif y % 2 == 0 and x % 2 == 1:
					(c1, c2) = (vchars[4], vchars[5])
				elif y % 2 == 1 and x % 2 == 1:
					(c1, c2) = (vchars[6], vchars[7])
				grid[2 * y][2 * x] = grid[2 * y + 1][2 * x] = c1
				grid[2 * y][2 * x + 1] = grid[2 * y + 1][2 * x + 1] = c2
	for row in grid:
		print(''.join(row))


for _ in range(int(input())):
	(n, m, k) = map(int, input().split())
	Ans = []
	for i in range(n):
		Ans.append([])
		for j in range(m):
			Ans[-1].append(0)
	if n % 2 == 1:
		if k < m // 2 or k % 2 != m // 2 % 2:
			print('NO')
		else:
			print('YES')
			for i in range(0, m - 1, 2):
				Ans[0][i] = chr(ord('a') + i % 26)
				Ans[0][i + 1] = chr(ord('a') + i % 26)
			for i in range(1, n - 1, 2):
				for j in range(0, m - 1, 2):
					if k - m // 2 > 0:
						Ans[i][j] = chr(ord('a') + (i + j) % 26)
						Ans[i][j + 1] = chr(ord('a') + (i + j) % 26)
						Ans[i + 1][j] = chr(ord('a') + (i + j + 1) % 26)
						Ans[i + 1][j + 1] = chr(ord('a') + (i + j + 1) % 26)
						k -= 2
					else:
						Ans[i][j] = chr(ord('a') + (i + j) % 26)
						Ans[i + 1][j] = chr(ord('a') + (i + j) % 26)
						Ans[i][j + 1] = chr(ord('a') + (i + j + 1) % 26)
						Ans[i + 1][j + 1] = chr(ord('a') + (i + j + 1) % 26)
			for i in range(len(Ans)):
				for j in range(len(Ans[i])):
					print(Ans[i][j], end='')
				print()
	elif k % 2 != 0 or k > n * (m // 2 * 2) // 2:
		print('NO')
	else:
		print('YES')
		for i in range(0, n - 1, 2):
			Ans[i][m - 1] = chr(ord('a') + (i + m - 1) % 26)
			Ans[i + 1][m - 1] = chr(ord('a') + (i + m - 1) % 26)
		for i in range(0, n - 1, 2):
			for j in range(0, m - 1, 2):
				if k > 0:
					Ans[i][j] = chr(ord('a') + (i + j) % 26)
					Ans[i][j + 1] = chr(ord('a') + (i + j) % 26)
					Ans[i + 1][j] = chr(ord('a') + (i + j + 1) % 26)
					Ans[i + 1][j + 1] = chr(ord('a') + (i + j + 1) % 26)
					k -= 2
				else:
					Ans[i][j] = chr(ord('a') + (i + j) % 26)
					Ans[i + 1][j] = chr(ord('a') + (i + j) % 26)
					Ans[i][j + 1] = chr(ord('a') + (i + j + 1) % 26)
					Ans[i + 1][j + 1] = chr(ord('a') + (i + j + 1) % 26)
		for i in range(len(Ans)):
			for j in range(len(Ans[i])):
				print(Ans[i][j], end='')
			print()


from __future__ import print_function
import math
from collections import deque
import os
import sys
from io import BytesIO, IOBase

def main():
	pass
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
mod = 10 ** 9 + 7

def inp():
	return int(input())

def inlt():
	return list(map(int, input().split()))

def insr():
	s = input()
	return list(s[:len(s)])

def invr():
	return map(int, input().split())
for _ in range(inp()):
	(n, m, k) = invr()
	if n % 2 == 0:
		r = 0
		out = []
		for i in range(n):
			out.append([])
		s = 0
		while True:
			if n <= k:
				k = k - n
				r += 2
				if s == 0:
					s = 1
					for i in range(0, n, 2):
						out[i].extend(['a', 'a'])
						out[i + 1].extend(['b', 'b'])
				else:
					s = 0
					for i in range(0, n, 2):
						out[i + 1].extend(['a', 'a'])
						out[i].extend(['b', 'b'])
			else:
				break
		if k == 0:
			print('YES')
			for i in range(r, m):
				if i % 2 == 0:
					for j in range(0, n, 2):
						if j % 4 == 0:
							out[j].append('c')
							out[j + 1].append('c')
						else:
							out[j + 1].append('d')
							out[j].append('d')
				else:
					for j in range(0, n, 2):
						if j % 4 != 0:
							out[j].append('c')
							out[j + 1].append('c')
						else:
							out[j + 1].append('d')
							out[j].append('d')
		else:
			if m - r < 2:
				print('NO')
				continue
			if k % 2 == 0:
				print('YES')
				if s == 0:
					s = 1
					for i in range(0, k, 2):
						out[i].extend(['a', 'a'])
						out[i + 1].extend(['b', 'b'])
				else:
					s = 0
					for i in range(0, k, 2):
						out[i + 1].extend(['a', 'a'])
						out[i].extend(['b', 'b'])
				for i in range(r, r + 2):
					if i % 2 == 0:
						for j in range(k, n, 2):
							if j % 4 == 0:
								out[j].append('x')
								out[j + 1].append('x')
							else:
								out[j + 1].append('y')
								out[j].append('y')
					else:
						for j in range(k, n, 2):
							if j % 4 == 0:
								out[j].append('y')
								out[j + 1].append('y')
							else:
								out[j + 1].append('x')
								out[j].append('x')
				r += 2
				for i in range(r, m):
					if i % 2 == 0:
						for j in range(0, n, 2):
							if j % 4 == 0:
								out[j].append('c')
								out[j + 1].append('c')
							else:
								out[j + 1].append('d')
								out[j].append('d')
					else:
						for j in range(0, n, 2):
							if j % 4 != 0:
								out[j].append('c')
								out[j + 1].append('c')
							else:
								out[j + 1].append('d')
								out[j].append('d')
			else:
				print('NO')
				continue
		for i in out:
			print(''.join((j for j in i)))
	else:
		k = n * m // 2 - k
		(n, m) = (m, n)
		r = 0
		out = []
		for i in range(n):
			out.append([])
		s = 0
		while True:
			if n <= k:
				k = k - n
				r += 2
				if s == 0:
					s = 1
					for i in range(0, n, 2):
						out[i].extend(['a', 'a'])
						out[i + 1].extend(['b', 'b'])
				else:
					s = 0
					for i in range(0, n, 2):
						out[i + 1].extend(['a', 'a'])
						out[i].extend(['b', 'b'])
			else:
				break
		if k == 0:
			print('YES')
			for i in range(r, m):
				if i % 2 == 0:
					for j in range(0, n, 2):
						if j % 4 == 0:
							out[j].append('c')
							out[j + 1].append('c')
						else:
							out[j + 1].append('d')
							out[j].append('d')
				else:
					for j in range(0, n, 2):
						if j % 4 != 0:
							out[j].append('c')
							out[j + 1].append('c')
						else:
							out[j + 1].append('d')
							out[j].append('d')
		else:
			if m - r < 2:
				print('NO')
				continue
			if k % 2 == 0:
				print('YES')
				if s == 0:
					s = 1
					for i in range(0, k, 2):
						out[i].extend(['a', 'a'])
						out[i + 1].extend(['b', 'b'])
				else:
					s = 0
					for i in range(0, k, 2):
						out[i + 1].extend(['a', 'a'])
						out[i].extend(['b', 'b'])
				for i in range(r, r + 2):
					if i % 2 == 0:
						for j in range(k, n, 2):
							if j % 4 == 0:
								out[j].append('x')
								out[j + 1].append('x')
							else:
								out[j + 1].append('y')
								out[j].append('y')
					else:
						for j in range(k, n, 2):
							if j % 4 == 0:
								out[j].append('y')
								out[j + 1].append('y')
							else:
								out[j + 1].append('x')
								out[j].append('x')
				r += 2
				for i in range(r, m):
					if i % 2 == 0:
						for j in range(0, n, 2):
							if j % 4 == 0:
								out[j].append('c')
								out[j + 1].append('c')
							else:
								out[j + 1].append('d')
								out[j].append('d')
					else:
						for j in range(0, n, 2):
							if j % 4 != 0:
								out[j].append('c')
								out[j + 1].append('c')
							else:
								out[j + 1].append('d')
								out[j].append('d')
			else:
				print('NO')
				continue
		for i in range(m):
			for j in range(n):
				print(out[j][i], end='')
			print('')


ans = []
for _ in range(int(input())):
	(n, m, k) = map(int, input().split())
	if n % 2 == 0 and m % 2 == 0:
		if k % 2 == 0:
			ans.append('YES')
			u = []
			for i in range(n):
				u.append(['a'] * m)
			a = b = 0
			cur = 'a'
			for i in range(k // 2):
				u[a][b] = cur
				u[a][b + 1] = cur
				cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
				u[a + 1][b] = cur
				u[a + 1][b + 1] = cur
				cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
				if b + 2 < m:
					b += 2
				else:
					b = 0
					a += 2
					cur = u[a - 1][b]
					cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
					cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
			for i in range(n * m // 4 - k // 2):
				u[a][b] = cur
				u[a + 1][b] = cur
				cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
				u[a][b + 1] = cur
				u[a + 1][b + 1] = cur
				cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
				if b + 2 < m:
					b += 2
				else:
					b = 0
					a += 2
					cur = u[a - 1][b]
					cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
					cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
			for i in range(n):
				ans.append(''.join(u[i]))
		else:
			ans.append('NO')
		continue
	ok = False
	if n % 2 == 1:
		k = n * m // 2 - k
		(n, m) = (m, n)
		ok = True
	if k > n * m // 2 - n // 2:
		ans.append('NO')
	elif k % 2 == 1:
		ans.append('NO')
	else:
		u = []
		for i in range(n):
			u.append(['a'] * m)
		cur = 'a'
		a = b = 0
		m -= 1
		for i in range(k // 2):
			u[a][b] = cur
			u[a][b + 1] = cur
			cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
			u[a + 1][b] = cur
			u[a + 1][b + 1] = cur
			cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
			if b + 2 < m:
				b += 2
			else:
				b = 0
				a += 2
				cur = u[a - 1][b]
				cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
				cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
		for i in range(n * m // 4 - k // 2):
			u[a][b] = cur
			u[a + 1][b] = cur
			cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
			u[a][b + 1] = cur
			u[a + 1][b + 1] = cur
			cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
			if b + 2 < m:
				b += 2
			else:
				b = 0
				a += 2
				cur = u[a - 1][b]
				cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
				cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
		m += 1
		for i in range(0, n, 2):
			if m == 1:
				if n == 2 or i == 0:
					cur = 'a'
				else:
					cur = u[i - 1][-1]
			else:
				cur = u[i][-2]
			cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
			cur = chr((ord(cur) - ord('a') + 1) % 26 + ord('a'))
			u[i][-1] = cur
			u[i + 1][-1] = cur
		ans.append('YES')
		if ok:
			w = []
			for i in range(m):
				w.append(['a'] * n)
			for i in range(n):
				for j in range(m):
					w[j][i] = u[i][j]
			for i in range(m):
				ans.append(''.join(w[i]))
		else:
			for i in range(n):
				ans.append(''.join(u[i]))
print('\n'.join(ans))


def paint(board, n, m, k):
	for i in range(n // 2):
		for j in range(m // 2):
			c = (i + j) % 3
			if k > 0:
				board[2 * i][2 * j] = c * 2
				board[2 * i][2 * j + 1] = c * 2
				board[2 * i + 1][2 * j] = c * 2 + 1
				board[2 * i + 1][2 * j + 1] = c * 2 + 1
				k -= 2
			else:
				board[2 * i][2 * j] = c * 2
				board[2 * i + 1][2 * j] = c * 2
				board[2 * i][2 * j + 1] = c * 2 + 1
				board[2 * i + 1][2 * j + 1] = c * 2 + 1

def h_paint(board, i, m, k):
	for j in range(m // 2):
		board[i][2 * j] = 10 + j % 2
		board[i][2 * j + 1] = 10 + j % 2

def v_paint(board, n, j, k):
	for i in range(n // 2):
		board[2 * i][j] = 12 + i % 2
		board[2 * i + 1][j] = 12 + i % 2

def print_b(board):
	for v in board:
		print(''.join(map(lambda x: chr(x + ord('a')), v)))
t = int(input())
for _ in range(t):
	(n, m, k) = list(map(int, input().split()))
	n2 = n - n % 2
	m2 = m - m % 2
	board = [m * [-1] for _ in range(n)]
	if k % 2 == 0:
		if n % 2:
			if m // 2 % 2 == 0 and k >= m // 2 and (m2 * n2 // 2 >= k - m // 2):
				print('YES')
				h_paint(board, -1, m2, k)
				k -= m2 // 2
				paint(board, n2, m2, k)
				print_b(board)
			else:
				print('NO')
		elif m2 * n2 // 2 >= k:
			print('YES')
			paint(board, n2, m2, k)
			if m % 2:
				v_paint(board, n, -1, k)
			print_b(board)
		else:
			print('NO')
	elif n % 2 and m // 2 % 2 and (m2 * n2 // 2 >= k - m // 2) and (k >= m // 2):
		print('YES')
		h_paint(board, -1, m2, k)
		k -= m2 // 2
		paint(board, n2, m2, k)
		print_b(board)
	else:
		print('NO')


from collections import *
import sys
input = sys.stdin.readline

def inp():
	return int(input())

def st():
	return input().rstrip('\n')

def lis():
	return list(map(int, input().split()))

def ma():
	return map(int, input().split())
t = inp()
gl = {'a': 'b', 'b': 'a'}
gl1 = {'c': 'd', 'd': 'c'}
while t:
	t -= 1
	(n, m, k) = ma()
	if n % 2 == m % 2 and n % 2 == 0:
		if k % 2:
			print('NO')
		else:
			print('YES')
			shift = 0
			if n % 4 == 0:
				shift = 1
			cur = 'a'
			res = [['$' for i in range(m)] for j in range(n)]
			for i in range(m):
				for j in range(0, n, 2):
					res[j][i] = cur
					res[j + 1][i] = cur
					cur = gl[cur]
				if shift:
					cur = gl[cur]
			shift = 0
			if m % 4 == 0:
				shift = 1
			cur = 'c'
			for i in range(0, m, 2):
				if k == 0:
					break
				for j in range(0, n):
					k -= 1
					res[j][i] = cur
					res[j][i + 1] = cur
					cur = gl1[cur]
					if k == 0:
						break
				if k == 0:
					break
				if 1:
					cur = gl1[cur]
			for i in res:
				print(''.join(i))
	elif 0:
		if m % 2:
			print('NO')
		else:
			print('YES')
		continue
	else:
		tot = k * 2
		if n % 2:
			re = k - m // 2
			if re >= 0 and re % 2 == 0:
				print('YES')
				shift = 0
				if (n - 1) % 4 == 0:
					shift = 1
				cur = 'a'
				res = [['$' for i in range(m)] for j in range(n)]
				for i in range(m):
					for j in range(1, n, 2):
						res[j][i] = cur
						res[j + 1][i] = cur
						cur = gl[cur]
					if shift:
						cur = gl[cur]
				cur = 'c'
				for i in range(0, m, 2):
					res[0][i] = cur
					res[0][i + 1] = cur
					cur = gl1[cur]
				k -= m // 2
				if m % 4 == 0:
					cur = gl1[cur]
				for i in range(1, n, 2):
					if k == 0:
						break
					for j in range(0, m, 2):
						k -= 2
						res[i][j] = cur
						res[i][j + 1] = cur
						cur = gl1[cur]
						res[i + 1][j] = cur
						res[i + 1][j + 1] = cur
						if k == 0:
							break
					if k == 0:
						break
					if m % 4:
						cur = gl1[cur]
				for i in res:
					print(''.join(i))
			else:
				print('NO')
		elif k % 2 == 0 and 2 * k <= n * (m - 1):
			print('YES')
			shift = 0
			if n % 4 == 0:
				shift = 1
			cur = 'a'
			res = [['$' for i in range(m)] for j in range(n)]
			for i in range(m):
				for j in range(0, n, 2):
					res[j][i] = cur
					res[j + 1][i] = cur
					cur = gl[cur]
				if shift:
					cur = gl[cur]
			shift = 0
			if m % 4 == 0:
				shift = 1
			cur = 'c'
			for i in range(0, m, 2):
				if k == 0:
					break
				for j in range(0, n):
					k -= 1
					res[j][i] = cur
					res[j][i + 1] = cur
					cur = gl1[cur]
					if k == 0:
						break
				if k == 0:
					break
				if 1:
					cur = gl1[cur]
			for i in res:
				print(''.join(i))
		else:
			print('NO')


import sys
from sys import stdin
alp = 'abcdefghijklmnopqrstuvwxyz'

def conv(lis):
	N = len(lis)
	M = len(lis[0])
	for i in range(N):
		for j in range(M):
			if lis[i][j] == '<':
				ts = set()
				for ni in range(i - 1, i + 2):
					for nj in range(j - 1, j + 3):
						if 0 <= ni < N and 0 <= nj < M and ('a' <= lis[ni][nj] <= 'z'):
							ts.add(lis[ni][nj])
				for c in alp:
					if c not in ts:
						lis[i][j] = c
						lis[i][j + 1] = c
						break
			if lis[i][j] == '^':
				ts = set()
				for ni in range(i - 1, i + 3):
					for nj in range(j - 1, j + 2):
						if 0 <= ni < N and 0 <= nj < M and ('a' <= lis[ni][nj] <= 'z'):
							ts.add(lis[ni][nj])
				for c in alp:
					if c not in ts:
						lis[i][j] = c
						lis[i + 1][j] = c
						break
	return lis

def solve(N, M, A, B):
	ans = [['.'] * M for i in range(N)]
	if N % 2 == 1:
		i = N - 1
		for j in range(1, M, 2):
			if A > 0:
				ans[i][j - 1] = '<'
				ans[i][j] = '>'
				A -= 1
	if M % 2 == 1:
		j = M - 1
		for i in range(1, N, 2):
			if B > 0:
				ans[i - 1][j] = '^'
				ans[i][j] = 'v'
				B -= 1
	for i in range(1, N, 2):
		for j in range(1, M, 2):
			if A >= 2:
				ans[i - 1][j - 1] = '<'
				ans[i - 1][j] = '>'
				ans[i][j - 1] = '<'
				ans[i][j] = '>'
				A -= 2
			elif A == 1:
				ans[i - 1][j - 1] = '<'
				ans[i - 1][j] = '>'
				A -= 1
			elif B >= 2:
				ans[i - 1][j - 1] = '^'
				ans[i - 1][j] = '^'
				ans[i][j - 1] = 'v'
				ans[i][j] = 'v'
				B -= 2
			elif B == 1:
				ans[i - 1][j - 1] = '^'
				ans[i][j - 1] = 'v'
				B -= 1
	if A + B == 0:
		print('YES')
		ans = conv(ans)
		for i in ans:
			pass
			print(''.join(i))
		return True
	return False

def solve2(N, M, A, B):
	ans = [['.'] * M for i in range(N)]
	ans[0][0] = '<'
	ans[0][1] = '>'
	ans[0][2] = '^'
	ans[1][0] = '^'
	ans[1][1] = '.'
	ans[1][2] = 'v'
	ans[2][0] = 'v'
	ans[2][1] = '<'
	ans[2][2] = '>'
	A -= 2
	B -= 2
	i = 0
	for j in range(M):
		if j + 1 < M and ans[i][j] == ans[i][j + 1] == '.' and (A >= 1):
			ans[i][j] = '<'
			ans[i][j + 1] = '>'
			A -= 1
	j = 0
	for i in range(N):
		if i + 1 < N and ans[i][j] == ans[i + 1][j] == '.' and (B >= 1):
			ans[i][j] = '^'
			ans[i + 1][j] = 'v'
			B -= 1
	for i in range(N):
		for j in range(M):
			if i + 1 < N and j + 1 < M and (ans[i][j] == ans[i + 1][j] == ans[i][j + 1] == ans[i + 1][j + 1] == '.') and (A >= 2):
				ans[i][j] = '<'
				ans[i][j + 1] = '>'
				ans[i + 1][j] = '<'
				ans[i + 1][j + 1] = '>'
				A -= 2
			elif i + 1 < N and j + 1 < M and (ans[i][j] == ans[i + 1][j] == ans[i][j + 1] == ans[i + 1][j + 1] == '.') and (B >= 2):
				ans[i][j] = '^'
				ans[i][j + 1] = '^'
				ans[i + 1][j] = 'v'
				ans[i + 1][j + 1] = 'v'
				B -= 2
			elif j + 1 < M and ans[i][j] == ans[i][j + 1] == '.' and (A >= 1):
				ans[i][j] = '<'
				ans[i][j + 1] = '>'
				A -= 1
			elif i + 1 < N and ans[i][j] == ans[i + 1][j] == '.' and (B >= 1):
				ans[i][j] = '^'
				ans[i + 1][j] = 'v'
				B -= 1
	if A + B > 0:
		print('NO')
		return False
	else:
		print('YES')
		ans = conv(ans)
		for i in ans:
			pass
			print(''.join(i))
		return True
tt = int(stdin.readline())
for loop in range(tt):
	(N, M, K) = map(int, stdin.readline().split())
	A = K
	B = N * M // 2 - A
	flag = solve(N, M, A, B)
	if flag:
		pass
	elif N >= 3 and M >= 3 and (A >= 2) and (B >= 2):
		solve2(N, M, A, B)
	else:
		print('NO')


import itertools
from dataclasses import dataclass

@dataclass
class TableView:
	line_length: int
	col_length: int

class DrawATable:
	VERTICAL_PIECE = 'abc'
	HORIZONTAL_PIECE = 'xyz'

	def __init__(self, n, m):
		self.n = n
		self.m = m
		self.table = list()
		for _ in range(self.n):
			self.table.append(['1'] * self.m)

	def gen(self, piece):
		yield from itertools.cycle(piece)

	def draw__vertical(self):
		src = self.gen(DrawATable.VERTICAL_PIECE)
		for row in range(self.n):
			for c in range(self.m):
				if self.table[row][c] != '1':
					continue
				pick = next(src)
				if row > 0 and self.table[row - 1][c] == pick:
					pick = next(src)
				if c > 0 and self.table[row][c - 1] == pick:
					pick = next(src)
				try:
					self.table[row][c] = pick
					self.table[row + 1][c] = pick
				except IndexError:
					pass

	def draw__horizontal(self, start_line, start_col, line_length, col_length, piece='xy'):
		src = self.gen(piece)
		for row in range(start_line, start_line + line_length):
			for c in range(start_col, start_col + col_length, 2):
				pick = next(src)
				if row > 0 and self.table[row - 1][c] == pick:
					pick = next(src)
				if c > 0 and self.table[row][c - 1] == pick:
					pick = next(src)
				try:
					self.table[row][c] = pick
					self.table[row][c + 1] = pick
				except IndexError:
					pass

	def render_table(self):
		for line in self.table:
			print(''.join(line))

def check_from_left_top_corner(n, m):
	for i in range(1, 1 + n):
		for j in range(2, m + 1, 2):
			if n - i & 1:
				continue
			if i & 1 and j < m:
				continue
			yield [i, j]

def check(n, m, k):
	for (w1, w2) in check_from_left_top_corner(n, m):
		if w1 * w2 == 2 * k:
			return ['YES', [TableView(w1, w2)]]
		if w1 < n and w2 < m:
			continue
		consumed = w1 * w2 // 2
		new_k = k - consumed
		table_views = [TableView(w1, w2)]
		for (w1, w2) in check_from_left_top_corner(n - w1, m):
			if w1 * w2 == 2 * new_k:
				table_views.append(TableView(w1, w2))
				return ['YES', table_views]
		for (w1, w2) in check_from_left_top_corner(n, m - w2):
			if w1 * w2 == 2 * new_k:
				table_views.append(TableView(w1, w2))
				return ['YES', table_views]
	return ['NO', []]

def solve():
	(n, m, k) = [int(x) for x in input().split()]
	a = DrawATable(n, m)
	if k == 0:
		if n & 1:
			print('NO')
			return
		print('YES')
		a.draw__vertical()
		a.render_table()
		return
	(ans, table_views) = check(n, m, k)
	if ans == 'YES':
		print('YES')
		if len(table_views) == 1:
			table_view = table_views[0]
			a.draw__horizontal(0, 0, table_view.line_length, table_view.col_length)
		else:
			assert len(table_views) == 2
			if table_views[0].line_length == n:
				a.draw__horizontal(0, 0, table_views[0].line_length, table_views[0].col_length)
				a.draw__horizontal(0, table_views[0].col_length, table_views[1].line_length, table_views[1].col_length, piece='ef')
			else:
				a.draw__horizontal(0, 0, table_views[1].line_length, table_views[1].col_length)
				a.draw__horizontal(table_views[1].line_length, 0, table_views[0].line_length, table_views[0].col_length, piece='ef')
		a.draw__vertical()
		a.render_table()
		return
	print('NO')
for _ in range(int(input())):
	solve()


def make(x, y, f):
	global res
	if len(res) > 0:
		x -= 1
	for i in range(x):
		res.append([0] * y)
	i = 0
	if res[0][0] != 0:
		i = 1
		x += 1
	j = 0
	while f >= x:
		f -= x - i
		for h in range(i, x):
			(res[h][j], res[h][j + 1]) = ('a', 'a') if res[h - 1][j] != 'a' and res[h][j - 1] != 'a' else ('b', 'b')
		j += 2
	while f > 0:
		(res[i][j], res[i][j + 1]) = ('a', 'a') if res[i - 1][j] != 'a' and res[i][j - 1] != 'a' else ('b', 'b')
		i += 1
		f -= 1
	h = 0
	while i + 1 < x and i != 0:
		(res[i][j], res[i + 1][j]) = ('c', 'c') if h % 2 == 0 else ('d', 'd')
		(res[i][j + 1], res[i + 1][j + 1]) = ('d', 'd') if h % 2 == 0 else ('c', 'c')
		h += 1
		i += 2
	if i > x:
		j += 2
	i = x - 2
	while j < y:
		while res[i][j] == 0:
			(res[i][j], res[i + 1][j]) = ('c', 'c') if res[i][j - 1] != 'c' and (not (i + 2 < x and res[i + 2][j] == 'c')) else ('d', 'd')
			i -= 2
		j += 1
		i = x - 2

def main():
	global res
	t = int(input())
	for i in range(t):
		(a, b, c) = map(int, input().split())
		res = []
		if c % 2 == 1 and a % 2 == 0:
			print('NO')
		elif a % 2 == 1:
			if b % 2 == 0:
				c -= b // 2
				if c % 2 == 1 or c < 0:
					print('NO')
				else:
					print('YES')
					make(b, a, a * b // 2 - (c + b // 2))
					for h in range(a):
						for h1 in range(b):
							print(res[h1][h], end='')
						print()
			else:
				print('NO')
		elif c % 2 == 0 and b % 2 == 1 and (c > a * (b - 1) // 2):
			print('NO')
		else:
			print('YES')
			make(a, b, c)
			for h in res:
				print(*h, sep='')
res = []
main()


def put_hor(x, y):
	symb = 'a' if (x // 2 + y) % 2 else 'b'
	fld[y][x:x + 2] = symb * 2

def put_ver(x, y):
	symb = 'c' if (x + y // 2) % 2 else 'd'
	fld[y][x] = symb
	fld[y + 1][x] = symb

def fill_hor(x0, y0, w, h):
	if h % 2 != 0:
		for i in range(0, w, 2):
			put_hor(x0 + i, y0)
		fill_hor(x0, y0 + 1, w, h - 1)
	else:
		for i in range(0, h, 2):
			for j in range(0, w, 2):
				put_hor(x0 + j, y0 + i)
				put_hor(x0 + j, y0 + i + 1)

def fill_ver(x0, y0, w, h):
	for i in range(0, h, 2):
		for j in range(w):
			put_ver(x0 + j, y0 + i)
import sys
input = lambda : sys.stdin.readline().rstrip('\r\n')
t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	hor_tiles = m // 2 * (n % 2)
	possible = m // 2 * n >= k >= hor_tiles and k % 2 == hor_tiles % 2
	print('YES' if possible else 'NO')
	if possible:
		fld = [['-' for _ in range(m + 1)] for _ in range(n + 1)]
		uneven_row = n % 2
		max_hor_fill = 2 * (m // 2)
		hor_full_rows_h = 0 if max_hor_fill == 0 else uneven_row + 2 * ((2 * k - uneven_row * max_hor_fill) // (2 * max_hor_fill))
		hor_part_rows_w = (2 * k - hor_full_rows_h * max_hor_fill) // 2
		ver_part_rows_w = m - hor_part_rows_w
		part_rows_h = 2 * (hor_part_rows_w > 0)
		ver_full_rows_h = n - hor_full_rows_h - part_rows_h
		uneven_column = m % 2
		fill_hor(1, 1, max_hor_fill, hor_full_rows_h)
		fill_hor(1, hor_full_rows_h + 1, hor_part_rows_w, part_rows_h)
		fill_ver(hor_part_rows_w + 1, hor_full_rows_h + 1, ver_part_rows_w, part_rows_h)
		fill_ver(1, hor_full_rows_h + 1 + part_rows_h, m, ver_full_rows_h)
		fill_ver(m, 1, uneven_column, n)
		print('\n'.join((''.join(r[1:]) for r in fld[1:])))


import sys
input = sys.stdin.readline

def main():
	(n, m, k) = map(int, input().split())
	x = n * m // 2 - k
	grid = [['.'] * m for _ in range(n)]
	if n % 2 == 0 and m % 2 == 0:
		if k % 2 == 1:
			print('NO')
			return
		print('YES')
		for i in range(0, n, 2):
			for j in range(0, m, 2):
				if (i + j) % 4 == 2:
					a = 'a'
					b = 'b'
				else:
					a = 'c'
					b = 'd'
				if k:
					k -= 2
					grid[i][j] = a
					grid[i][j + 1] = a
					grid[i + 1][j] = b
					grid[i + 1][j + 1] = b
				else:
					grid[i][j] = a
					grid[i][j + 1] = b
					grid[i + 1][j] = a
					grid[i + 1][j + 1] = b
		for row in grid:
			print(''.join(row))
		return
	if n % 2 == 0:
		if x < n // 2:
			print('NO')
			return
		x -= n // 2
		if x % 2 == 1:
			print('NO')
			return
		for i in range(0, n, 2):
			if i % 4 == 2:
				a = 'e'
			else:
				a = 'f'
			grid[i][0] = a
			grid[i + 1][0] = a
		print('YES')
		for i in range(0, n, 2):
			for j in range(1, m, 2):
				if (i + j) % 4 == 1:
					a = 'a'
					b = 'b'
				else:
					a = 'c'
					b = 'd'
				if k:
					k -= 2
					grid[i][j] = a
					grid[i][j + 1] = a
					grid[i + 1][j] = b
					grid[i + 1][j + 1] = b
				else:
					grid[i][j] = a
					grid[i][j + 1] = b
					grid[i + 1][j] = a
					grid[i + 1][j + 1] = b
		for row in grid:
			print(''.join(row))
		return
	else:
		if k < m // 2:
			print('NO')
			return
		k -= m // 2
		if x % 2 == 1:
			print('NO')
			return
		for j in range(0, m, 2):
			if j % 4 == 2:
				a = 'e'
			else:
				a = 'f'
			grid[0][j] = a
			grid[0][j + 1] = a
		print('YES')
		for i in range(1, n, 2):
			for j in range(0, m, 2):
				if (i + j) % 4 == 1:
					a = 'a'
					b = 'b'
				else:
					a = 'c'
					b = 'd'
				if k:
					k -= 2
					grid[i][j] = a
					grid[i][j + 1] = a
					grid[i + 1][j] = b
					grid[i + 1][j + 1] = b
				else:
					grid[i][j] = a
					grid[i][j + 1] = b
					grid[i + 1][j] = a
					grid[i + 1][j + 1] = b
		for row in grid:
			print(''.join(row))
		return
for _ in range(int(input())):
	main()


import os, sys
from io import BytesIO, IOBase
from math import log2, ceil, sqrt, gcd
from _collections import deque
import heapq as hp
from bisect import bisect_left, bisect_right
from math import cos, sin
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
mod = 10 ** 9 + 7

def solve1(n, m, k):
	ar = ['a', 'b']
	t = 0
	for i in range(0, m, 2):
		if k:
			a[0][i] = ar[t]
			a[0][i + 1] = ar[t]
			k[0] -= 1
			t ^= 1

def solve2(n, m, k):
	ar = ['a', 'b']
	t = 0
	for i in range(0, n, 2):
		a[i][0] = ar[t]
		a[i + 1][0] = ar[t]
		t ^= 1

def get_char(i, j):
	s = set()
	if j - 1 >= 0:
		s.add(a[i][j - 1])
		s.add(a[i + 1][j - 1])
	if i - 1 >= 0:
		s.add(a[i - 1][j])
		s.add(a[i - 1][j + 1])
	r = []
	for i in range(97, 123):
		if chr(i) not in s:
			r.append(chr(i))
		if len(r) >= 2:
			return r

def get_char1(i, j):
	s = set()
	if j - 1 >= 0:
		s.add(a[i][j - 1])
		s.add(a[i + 1][j - 1])
	if i - 1 >= 0:
		s.add(a[i - 1][j])
	r = []
	for i in range(97, 123):
		if chr(i) not in s:
			r.append(chr(i))
		if r:
			return r

def solve(n, m, k):
	for i in range(n):
		for j in range(m):
			if a[i][j] == '.':
				if k[0] >= 2 and i + 1 < n and (j + 1 < m):
					r = get_char(i, j)
					a[i][j] = r[0]
					a[i][j + 1] = r[0]
					k[0] -= 1
					a[i + 1][j] = r[1]
					a[i + 1][j + 1] = r[1]
					k[0] -= 1
				elif i + 1 < n:
					r = get_char1(i, j)
					a[i][j] = r[0]
					a[i + 1][j] = r[0]
for _ in range(int(input())):
	(n, m, k1) = map(int, input().split())
	k = [k1]
	a = [['.'] * m for _ in range(n)]
	if n % 2:
		solve1(n, m, k)
	if m % 2:
		solve2(n, m, k)
	solve(n, m, k)
	ans = True
	for i in range(n):
		for j in range(m):
			if a[i][j] == '.':
				ans = False
				break
	if ans and k[0] == 0:
		print('YES')
		for i in a:
			print(''.join(i))
	else:
		print('NO')


import os
import sys
from collections import *
from bisect import *
from io import BytesIO, IOBase

def vsInput():
	sys.stdin = open('input.txt', 'r')
	sys.stdout = open('output.txt', 'w')
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
ALPHA = 'abcdefghijklmnopqrstuvwxyz'
M = 10 ** 9 + 7
EPS = 1e-06

def Ceil(a, b):
	return a // b + int(a % b > 0)

def value():
	return tuple(map(int, input().split()))

def array():
	return [int(i) for i in input().split()]

def Int():
	return int(input())

def Str():
	return input()

def arrayS():
	return [i for i in input().split()]

def GetH(i, j):
	for ch in ALPHA:
		ok = True
		if j - 1 >= 0 and ans[i][j - 1] == ch:
			ok = False
		if i - 1 >= 0 and ans[i - 1][j] == ch:
			ok = False
		if i - 1 >= 0 and j + 1 < m and (ans[i - 1][j + 1] == ch):
			ok = False
		if ok:
			return ch
	return -1

def GetV(i, j):
	for ch in ALPHA:
		ok = True
		if j - 1 >= 0 and ans[i][j - 1] == ch:
			ok = False
		if i - 1 >= 0 and ans[i - 1][j] == ch:
			ok = False
		if j - 1 >= 0 and i + 1 < n and (ans[i + 1][j - 1] == ch):
			ok = False
		if ok:
			return ch
	return -1
for _ in range(Int()):
	(n, m, k) = value()
	ans = [[0 for i in range(m)] for j in range(n)]
	if n % 2:
		for i in range(0, m, 2):
			ans[0][i] = ans[0][i + 1] = GetH(0, i)
		k -= m // 2
	for i in range(n % 2, n, 2):
		for j in range(0, m, 2):
			if k > 0 and j + 1 < m:
				k -= 2
				ans[i][j] = ans[i][j + 1] = GetH(i, j)
				ans[i + 1][j] = ans[i + 1][j + 1] = GetH(i + 1, j)
	if k == 0:
		print('YES')
		for i in range(n):
			for j in range(m):
				if ans[i][j] == 0:
					ans[i][j] = ans[i + 1][j] = GetV(i, j)
			print(*ans[i], sep='')
	else:
		print('NO')


alp = 'abcdefg'

def provide(se):
	for i in alp:
		if not i in se:
			return i

def create(n, m, k, ar):
	count = 0
	for i in range(n):
		ar.append(['@'] * m)
	for i in range(0, m, 2):
		ar[0][i] = alp[count % 6]
		ar[0][i + 1] = alp[count % 6]
		k -= 1
		count += 1
	i = 1
	while i < n:
		j = 0
		while j < m:
			if k:
				se = {ar[i - 1][j], ar[i - 1][j + 1]}
				if j != 0:
					se.add(ar[i][j - 1])
				ar[i][j] = provide(se)
				ar[i][j + 1] = provide(se)
				count += 1
				se = {ar[i][j], ar[i][j + 1]}
				if j != 0:
					se.add(ar[i + 1][j - 1])
				ar[i + 1][j] = provide(se)
				ar[i + 1][j + 1] = provide(se)
				count += 1
				k -= 2
			else:
				se = {ar[i - 1][j]}
				if j != 0:
					se.add(ar[i][j - 1])
					se.add(ar[i + 1][j - 1])
				ar[i][j] = provide(se)
				ar[i + 1][j] = provide(se)
				count += 1
				se = {ar[i - 1][j + 1], ar[i][j], ar[i + 1][j]}
				ar[i][j + 1] = provide(se)
				ar[i + 1][j + 1] = provide(se)
				count += 1
			j += 2
		i += 2
for _ in range(int(input())):
	(n, m, k) = map(int, input().split())
	flag = False
	if n % 2 != 0:
		if k >= m // 2 and (k - m // 2) % 2 == 0:
			flag = True
		if flag:
			print('YES')
			ar = []
			create(n, m, k, ar)
			for i in ar:
				print(''.join(i))
		else:
			print('NO')
	elif m % 2 != 0:
		(n, m) = (m, n)
		k = n * m // 2 - k
		if k >= m // 2 and (k - m // 2) % 2 == 0:
			flag = True
		if flag:
			print('YES')
			ar = []
			create(n, m, k, ar)
			br = []
			for i in range(m):
				br.append(['@'] * n)
			for i in range(n):
				for j in range(m):
					br[j][i] = ar[i][j]
			for i in br:
				print(''.join(i))
		else:
			print('NO')
	else:
		if k % 2 == 0:
			flag = True
		if flag:
			print('YES')
			count = 0
			ar = []
			for i in range(n):
				ar.append(['@'] * m)
			for i in range(0, n, 2):
				for j in range(0, m, 2):
					if k:
						se = {ar[i - 1][j], ar[i - 1][j + 1]}
						if j != 0:
							se.add(ar[i][j - 1])
						ar[i][j] = provide(se)
						ar[i][j + 1] = provide(se)
						count += 1
						se = {ar[i][j], ar[i][j + 1]}
						if j != 0:
							se.add(ar[i + 1][j - 1])
						ar[i + 1][j] = provide(se)
						ar[i + 1][j + 1] = provide(se)
						count += 1
						k -= 2
					else:
						se = {ar[i - 1][j]}
						if j != 0:
							se.add(ar[i][j - 1])
							se.add(ar[i + 1][j - 1])
						ar[i][j] = provide(se)
						ar[i + 1][j] = provide(se)
						count += 1
						se = {ar[i - 1][j + 1], ar[i][j], ar[i + 1][j]}
						ar[i][j + 1] = provide(se)
						ar[i + 1][j + 1] = provide(se)
						count += 1
			for i in ar:
				print(''.join(i))
		else:
			print('NO')


t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	if n % 2 == m % 2 == 0:
		if k % 2 == 0:
			print('YES')
			ans = [[0] * (m + 2) for _ in range(n + 2)]
			cnt = 0
			j = 1
			moji = 0
			while cnt < k:
				for i in range(1, n + 1):
					while ans[i - 1][j] == chr(97 + moji % 26) or ans[i][j - 1] == chr(97 + moji % 26):
						moji += 1
					ans[i][j] = chr(97 + moji % 26)
					ans[i][j + 1] = chr(97 + moji % 26)
					cnt += 1
					if cnt == k:
						break
				j += 2
			i = 1
			while i < n + 1:
				for j in range(1, m + 1):
					if ans[i][j] == 0:
						while ans[i - 1][j] == chr(97 + moji % 26) or ans[i][j - 1] == chr(97 + moji % 26) or ans[i + 1][j - 1] == chr(97 + moji % 26):
							moji += 1
						ans[i][j] = chr(97 + moji % 26)
						ans[i + 1][j] = chr(97 + moji % 26)
				i += 2
			for x in ans[1:n + 1]:
				print(''.join(x[1:m + 1]))
		else:
			print('NO')
	elif n % 2 == 0:
		if (n * m - 2 * k) // 2 - n // 2 >= 0 and ((n * m - 2 * k) // 2 - n // 2) % 2 == 0:
			print('YES')
			ans = [[0] * (m + 2) for _ in range(n + 2)]
			i = 1
			moji = 0
			while i <= n:
				while ans[i - 1][1] == chr(97 + moji % 26):
					moji += 1
				ans[i][1] = chr(97 + moji % 26)
				ans[i + 1][1] = chr(97 + moji % 26)
				i += 2
			K = (n * m - 2 * k) // 2 - n // 2
			cnt = 0
			i = 1
			while cnt < K:
				for j in range(2, m + 1):
					while ans[i - 1][j] == chr(97 + moji % 26) or ans[i][j - 1] == chr(97 + moji % 26):
						moji += 1
					ans[i][j] = chr(97 + moji % 26)
					ans[i + 1][j] = chr(97 + moji % 26)
					cnt += 1
					if cnt == K:
						break
				i += 2
			for i in range(1, n + 1):
				for j in range(1, m + 1):
					if ans[i][j] == 0:
						while ans[i - 1][j] == chr(97 + moji % 26) or ans[i][j - 1] == chr(97 + moji % 26) or ans[i - 1][j + 1] == chr(97 + moji % 26):
							moji += 1
						ans[i][j] = chr(97 + moji % 26)
						ans[i][j + 1] = chr(97 + moji % 26)
			for x in ans[1:n + 1]:
				print(''.join(x[1:m + 1]))
		else:
			print('NO')
	elif k - m // 2 >= 0 and (k - m // 2) % 2 == 0:
		print('YES')
		ans = [[0] * (m + 2) for _ in range(n + 2)]
		j = 1
		moji = 0
		while j <= m:
			while ans[1][j - 1] == chr(97 + moji % 26):
				moji += 1
			ans[1][j] = chr(97 + moji % 26)
			ans[1][j + 1] = chr(97 + moji % 26)
			j += 2
		k = k - m // 2
		cnt = 0
		j = 1
		while cnt < k:
			for i in range(2, n + 1):
				while ans[i - 1][j] == chr(97 + moji % 26) or ans[i][j - 1] == chr(97 + moji % 26):
					moji += 1
				ans[i][j] = chr(97 + moji % 26)
				ans[i][j + 1] = chr(97 + moji % 26)
				cnt += 1
				if cnt == k:
					break
			j += 2
		i = 2
		while i < n + 1:
			for j in range(1, m + 1):
				if ans[i][j] == 0:
					while ans[i - 1][j] == chr(97 + moji % 26) or ans[i][j - 1] == chr(97 + moji % 26) or ans[i + 1][j - 1] == chr(97 + moji % 26):
						moji += 1
					ans[i][j] = chr(97 + moji % 26)
					ans[i + 1][j] = chr(97 + moji % 26)
			i += 2
		for x in ans[1:n + 1]:
			print(''.join(x[1:m + 1]))
	else:
		print('NO')


mod = 10 ** 9 + 7

def gcd(a, b):
	return a if b == 0 else gcd(b, a % b)

def lcm(a, b):
	return a * b // gcd(a, b)

def solve(t_id):
	(n, m, k) = map(int, input().split())
	ok = False
	swapped = False
	if m % 2 > 0:
		(n, m) = (m, n)
		k = m * n // 2 - k
		swapped = True
	ans = [['*' for i in range(m)] for j in range(n)]
	if n % 2 > 0 and k >= m // 2 and ((k - m // 2) % 2 == 0) and (n * m // 2 - k <= m * (n // 2)):
		ok = True
		for j in range(0, m, 2):
			for i in range(1):
				if k > 0:
					ans[i][j] = chr(ord('a') + (i % 3 * 3 + j // 2 % 3))
					ans[i][j + 1] = chr(ord('a') + (i % 3 * 3 + j // 2 % 3))
					k -= 1
		for j in range(0, m, 2):
			for i in range(1, n):
				if k > 0:
					ans[i][j] = chr(ord('a') + (i % 3 * 3 + j // 2 % 3))
					ans[i][j + 1] = chr(ord('a') + (i % 3 * 3 + j // 2 % 3))
					k -= 1
		for i in range(1, n, 2):
			for j in range(m):
				if ans[i][j] == '*':
					ans[i][j] = chr(13 + ord('a') + (i // 2 % 3 * 3 + j % 3))
					ans[i + 1][j] = chr(13 + ord('a') + (i // 2 % 3 * 3 + j % 3))
	elif n % 2 == 0 and m % 2 == 0 and ((n - k % n) % 2 == 0):
		ok = True
		for j in range(0, m, 2):
			for i in range(n):
				if k > 0:
					ans[i][j] = chr(ord('a') + (i % 3 * 3 + j // 2 % 3))
					ans[i][j + 1] = chr(ord('a') + (i % 3 * 3 + j // 2 % 3))
					k -= 1
		for i in range(0, n, 2):
			for j in range(m):
				if ans[i][j] == '*':
					ans[i][j] = chr(13 + ord('a') + (i // 2 % 3 * 3 + j % 3))
					ans[i + 1][j] = chr(13 + ord('a') + (i // 2 % 3 * 3 + j % 3))
	print('YES' if ok else 'NO')
	if ok:
		if swapped:
			tmp = [['*' for i in range(n)] for j in range(m)]
			for i in range(n):
				for j in range(m):
					tmp[j][i] = ans[i][j]
			ans = tmp
			(n, m) = (m, n)
		for i in range(n):
			print(*ans[i], sep='')
t = 1
t = int(input())
for i in range(t):
	solve(i + 1)


import sys
input = sys.stdin.readline
t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	if n % 2 == m % 2 == 0:
		ans = 'YES' if k % 2 == 0 else 'NO'
		if ans == 'YES':
			s = [['?'] * m for _ in range(n)]
			for i in range(n // 2):
				for j in range(m // 2):
					if (i + j) % 2:
						if k:
							s[2 * i][2 * j] = 'a'
							s[2 * i + 1][2 * j] = 'b'
							s[2 * i][2 * j + 1] = 'a'
							s[2 * i + 1][2 * j + 1] = 'b'
							k -= 2
						else:
							s[2 * i][2 * j] = 'a'
							s[2 * i + 1][2 * j] = 'a'
							s[2 * i][2 * j + 1] = 'b'
							s[2 * i + 1][2 * j + 1] = 'b'
					elif k:
						s[2 * i][2 * j] = 'c'
						s[2 * i + 1][2 * j] = 'd'
						s[2 * i][2 * j + 1] = 'c'
						s[2 * i + 1][2 * j + 1] = 'd'
						k -= 2
					else:
						s[2 * i][2 * j] = 'c'
						s[2 * i + 1][2 * j] = 'c'
						s[2 * i][2 * j + 1] = 'd'
						s[2 * i + 1][2 * j + 1] = 'd'
	elif n % 2 == 1:
		if k < m // 2:
			ans = 'NO'
		else:
			ans = 'YES' if (k - m // 2) % 2 == 0 else 'NO'
		if ans == 'YES':
			s = [['?'] * m for _ in range(n)]
			for i in range(m // 2):
				if i % 2:
					s[n - 1][2 * i] = 'e'
					s[n - 1][2 * i + 1] = 'e'
				else:
					s[n - 1][2 * i] = 'f'
					s[n - 1][2 * i + 1] = 'f'
				k -= 1
			for i in range(n // 2):
				for j in range(m // 2):
					if (i + j) % 2:
						if k:
							s[2 * i][2 * j] = 'a'
							s[2 * i + 1][2 * j] = 'b'
							s[2 * i][2 * j + 1] = 'a'
							s[2 * i + 1][2 * j + 1] = 'b'
							k -= 2
						else:
							s[2 * i][2 * j] = 'a'
							s[2 * i + 1][2 * j] = 'a'
							s[2 * i][2 * j + 1] = 'b'
							s[2 * i + 1][2 * j + 1] = 'b'
					elif k:
						s[2 * i][2 * j] = 'c'
						s[2 * i + 1][2 * j] = 'd'
						s[2 * i][2 * j + 1] = 'c'
						s[2 * i + 1][2 * j + 1] = 'd'
						k -= 2
					else:
						s[2 * i][2 * j] = 'c'
						s[2 * i + 1][2 * j] = 'c'
						s[2 * i][2 * j + 1] = 'd'
						s[2 * i + 1][2 * j + 1] = 'd'
	else:
		(n, m) = (m, n)
		k = n * m // 2 - k
		if k < m // 2:
			ans = 'NO'
		else:
			ans = 'YES' if (k - m // 2) % 2 == 0 else 'NO'
		if ans == 'YES':
			s = [['?'] * n for _ in range(m)]
			for i in range(m // 2):
				if i % 2:
					s[2 * i][n - 1] = 'e'
					s[2 * i + 1][n - 1] = 'e'
				else:
					s[2 * i][n - 1] = 'f'
					s[2 * i + 1][n - 1] = 'f'
				k -= 1
			for i in range(m // 2):
				for j in range(n // 2):
					if (i + j) % 2:
						if not k:
							s[2 * i][2 * j] = 'a'
							s[2 * i + 1][2 * j] = 'b'
							s[2 * i][2 * j + 1] = 'a'
							s[2 * i + 1][2 * j + 1] = 'b'
						else:
							s[2 * i][2 * j] = 'a'
							s[2 * i + 1][2 * j] = 'a'
							s[2 * i][2 * j + 1] = 'b'
							s[2 * i + 1][2 * j + 1] = 'b'
							k -= 2
					elif not k:
						s[2 * i][2 * j] = 'c'
						s[2 * i + 1][2 * j] = 'd'
						s[2 * i][2 * j + 1] = 'c'
						s[2 * i + 1][2 * j + 1] = 'd'
					else:
						s[2 * i][2 * j] = 'c'
						s[2 * i + 1][2 * j] = 'c'
						s[2 * i][2 * j + 1] = 'd'
						s[2 * i + 1][2 * j + 1] = 'd'
						k -= 2
	print(ans)
	if ans == 'YES':
		for s0 in s:
			print(''.join(s0))


def solve():
	(n, m, k) = [int(x) for x in input().split()]
	vert_k = n * m // 2 - k
	arr = [[0 for i in range(m)] for j in range(n)]
	(j1, j2) = [0, 1]

	def ok(x, y):
		if x >= 0 and y >= 0 and (x < n) and (y < m):
			return True
		else:
			return False

	def get_col(x1, y1, x2, y2):
		st = set(['a', 'b', 'c', 'd', 'e', 'f'])
		dx = [0, 1, -1, 0]
		dy = [1, 0, 0, -1]
		for k in range(4):
			u = x1 + dx[k]
			v = y1 + dy[k]
			if ok(u, v):
				if arr[u][v] in st:
					st.remove(arr[u][v])
			u = x2 + dx[k]
			v = y2 + dy[k]
			if ok(u, v):
				if arr[u][v] in st:
					st.remove(arr[u][v])
		return list(st)[0]
	if n % 2 == 1:
		for j in range(0, m, 2):
			if k > 0 and j + 1 < m:
				arr[0][j] = arr[0][j + 1] = get_col(0, j, 0, j + 1)
				k -= 1
	while j2 < m and k > 0:
		for i in range(n):
			col = get_col(i, j1, i, j2)
			if arr[i][j1] != 0:
				continue
			if k == 0:
				break
			elif k == 1:
				if (n - i - 1) % 2 == 0:
					arr[i][j1] = arr[i][j2] = col
					k -= 1
				else:
					break
			else:
				arr[i][j1] = arr[i][j2] = col
				k -= 1
		j1 = j2 + 1
		j2 = j1 + 1
	k = vert_k
	(i1, i2) = [0, 1]
	while i2 < n and k > 0:
		for j in range(m):
			if k == 0:
				break
			if arr[i1][j] == 0 and arr[i2][j] == 0:
				arr[i1][j] = arr[i2][j] = get_col(i1, j, i2, j)
				k -= 1
		i1 = i2
		i2 = i1 + 1
	ct = 0
	for x in arr:
		ct += x.count(0)
	if ct == 0:
		print('YES')
		for x in arr:
			print(*x, sep='')
	else:
		print('NO')

def main():
	for case in range(int(input())):
		solve()
py2 = round(0.5)
if py2:
	from future_builtins import ascii, filter, hex, map, oct, zip
	range = xrange
import os, sys
from io import IOBase, BytesIO
BUFSIZE = 8192

class FastIO(BytesIO):
	newlines = 0

	def __init__(self, file):
		self._file = file
		self._fd = file.fileno()
		self.writable = 'x' in file.mode or 'w' in file.mode
		self.write = super(FastIO, self).write if self.writable else None

	def _fill(self):
		s = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
		self.seek((self.tell(), self.seek(0, 2), super(FastIO, self).write(s))[0])
		return s

	def read(self):
		while self._fill():
			pass
		return super(FastIO, self).read()

	def readline(self):
		while self.newlines == 0:
			s = self._fill()
			self.newlines = s.count(b'\n') + (not s)
		self.newlines -= 1
		return super(FastIO, self).readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.getvalue())
			(self.truncate(0), self.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		if py2:
			self.write = self.buffer.write
			self.read = self.buffer.read
			self.readline = self.buffer.readline
		else:
			self.write = lambda s: self.buffer.write(s.encode('ascii'))
			self.read = lambda : self.buffer.read().decode('ascii')
			self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
main()


from string import ascii_lowercase

def surrounding(i1, j1, i2, j2):
	k = []
	for da in range(-1, 2):
		for db in range(-1, 2):
			k.append((i1 + da, j1 + db))
			k.append((i2 + da, j2 + db))
	k = [(a, b) for (a, b) in k if 0 <= a < n and 0 <= b < m]
	return list(set(k))

def link(i1, j1, i2, j2):
	s = [ans[a][b] for (a, b) in surrounding(i1, j1, i2, j2)]
	for f in ascii_lowercase:
		if f not in s:
			break
	ans[i1][j1] = ans[i2][j2] = f
for _ in range(int(input())):
	(n, m, k) = map(int, input().split())
	if n % 2 == 0 and m % 2 == 0:
		if k % 2:
			print('NO')
			continue
		print('YES')
		ans = [['.'] * m for _ in range(n)]
		for i in range(n):
			for j in range(m):
				if k == 0:
					break
				if ans[i][j] != '.':
					continue
				link(i, j, i, j + 1)
				link(i + 1, j, i + 1, j + 1)
				k -= 2
			if k == 0:
				break
		for i in range(n):
			for j in range(m):
				if ans[i][j] != '.':
					continue
				link(i, j, i + 1, j)
		for line in ans:
			print(*line, sep='')
		continue
	if m % 2:
		flip = True
		(n, m, k) = (m, n, m * n // 2 - k)
	else:
		flip = False
	if k - m // 2 < 0 or (k - m // 2) % 2 == 1:
		print('NO')
		continue
	print('YES')
	ans = [['.'] * m for _ in range(n)]
	for j in range(m):
		if ans[0][j] != '.':
			continue
		link(0, j, 0, j + 1)
		k -= 1
	for i in range(n):
		for j in range(m):
			if k == 0:
				break
			if ans[i][j] != '.':
				continue
			link(i, j, i, j + 1)
			link(i + 1, j, i + 1, j + 1)
			k -= 2
		if k == 0:
			break
	for i in range(n):
		for j in range(m):
			if ans[i][j] != '.':
				continue
			link(i, j, i + 1, j)
	if not flip:
		for line in ans:
			print(*line, sep='')
		continue
	for j in range(m):
		for i in range(n):
			print(ans[i][j], end='')
		print()


letters = 'abcdefghijklmnopqrstuvw'
boundary = 'xy'

def get(point, n, m, table):
	ptr = 0
	while True:
		if check(point, letters[ptr], n, m, table):
			yield letters[ptr]
		ptr += 1
		if ptr == len(letters):
			ptr = 0

def get_boundary():
	for ii in range(0, 1000):
		yield boundary[ii % 2]

def check(point, color, n, m, table):
	relative = [(0, 1), (1, 0), (-1, 0), (0, -1), (1, 1), (1, -1), (-1, -1), (-1, 1)]
	for pnt in relative:
		(x, y) = (point[0] + pnt[0], point[1] + pnt[1])
		if 0 <= x < n and 0 <= y < m:
			if table[x][y] == color:
				return False
	return True

def solve(n, m, k):
	(vertical, horizontal) = (m * n // 2 - k, k)
	color_boundary = get_boundary()
	table = [['-' for _ in range(m)] for _ in range(n)]
	if n % 2 == 1:
		if horizontal < m // 2:
			return False
		horizontal -= m // 2
		for ii in range(0, m, 2):
			table[n - 1][ii] = table[n - 1][ii + 1] = next(color_boundary)
		n -= 1
	if m % 2 == 1:
		if vertical < n // 2:
			return False
		vertical -= n // 2
		for ii in range(0, n, 2):
			table[ii][m - 1] = table[ii + 1][m - 1] = next(color_boundary)
		m -= 1
	if vertical % 2 != 0:
		return False
	for ii in range(0, n, 2):
		for jj in range(0, m, 2):
			if horizontal > 0:
				horizontal -= 2
				char = get(point=[ii, jj], n=n, m=m, table=table)
				table[ii][jj] = table[ii][jj + 1] = next(char)
				char = get(point=[ii + 1, jj], n=n, m=m, table=table)
				table[ii + 1][jj] = table[ii + 1][jj + 1] = next(char)
			else:
				vertical -= 2
				char = get(point=[ii, jj], n=n, m=m, table=table)
				table[ii][jj] = table[ii + 1][jj] = next(char)
				char = get(point=[ii, jj + 1], n=n, m=m, table=table)
				table[ii][jj + 1] = table[ii + 1][jj + 1] = next(char)
	return table

def main():
	t = int(input())
	for _ in range(t):
		(n, m, k) = list(map(int, input().split()))
		answ = solve(n, m, k)
		if answ is False:
			print('NO')
		else:
			print('YES')
			for line in answ:
				print(''.join(line))
main()


import math
import heapq
import string
from collections import deque
import sys
input = sys.stdin.readline
S = lambda : input()
I = lambda : int(S())
M = lambda : map(int, S().split())
L = lambda : list(M())
H = 1000000000 + 7
for _ in range(I()):
	(n, m, k) = M()

	def pri(dp, n, m):
		for i in range(n):
			s = ''
			for j in range(m):
				s += dp[i][j]
			print(s)

	def trans(dp, n, m):
		dp1 = [[0 for i in range(n)] for j in range(m)]
		for j in range(m):
			for i in range(n):
				dp1[j][i] = dp[i][j]
		return dp1

	def solve(a, n, m, k, dp, c):
		i = a
		j = 0
		for i in range(a, n, 2):
			for j in range(0, m, 2):
				if c >= k:
					break
				s = (i // 2 + j // 2) % 2
				dp[i][j] = chr(2 * s + 97)
				dp[i][j + 1] = chr(2 * s + 97)
				dp[i + 1][j] = chr(2 * s + 1 + 97)
				dp[i + 1][j + 1] = chr(2 * s + 1 + 97)
				c += 2
			if c >= k:
				break
		if i < n and j < m and (dp[i][j] == 0):
			for r in range(j, m, 2):
				if c >= n * m // 2:
					break
				s = (i // 2 + r // 2) % 2
				dp[i][r] = chr(2 * s + 97)
				dp[i + 1][r] = chr(2 * s + 97)
				dp[i][r + 1] = chr(2 * s + 1 + 97)
				dp[i + 1][r + 1] = chr(2 * s + 1 + 97)
				s ^= 1
				c += 2
		for t in range(i + 2, n, 2):
			for j in range(0, m, 2):
				if c >= n * m // 2:
					break
				s = (t // 2 + j // 2) % 2
				dp[t][j] = chr(2 * s + 97)
				dp[t + 1][j] = chr(2 * s + 97)
				dp[t][j + 1] = chr(2 * s + 1 + 97)
				dp[t + 1][j + 1] = chr(2 * s + 1 + 97)
				s ^= 1
				c += 2
			if c >= n * m // 2:
				break
	if n % 2 == 0 and m % 2 == 0:
		dp = [[0 for i in range(m)] for j in range(n)]
		if k % 2 == 0:
			print('YES')
			solve(0, n, m, k, dp, 0)
			pri(dp, n, m)
		else:
			print('NO')
	elif n % 2 == 0 and m % 2 == 1:
		k = n * m // 2 - k
		(n, m) = (m, n)
		dp = [[0 for i in range(m)] for j in range(n)]
		if k >= m // 2 and (k - m // 2) % 2 == 0:
			print('YES')
			s = c = 0
			for j in range(0, m, 2):
				dp[0][j] = chr(s + 121)
				dp[0][j + 1] = chr(s + 121)
				s ^= 1
				c += 1
			solve(1, n, m, k, dp, c)
			dp1 = trans(dp, n, m)
			pri(dp1, m, n)
		else:
			print('NO')
	else:
		dp = [[0 for i in range(m)] for j in range(n)]
		if k >= m // 2 and (k - m // 2) % 2 == 0:
			print('YES')
			s = c = 0
			for j in range(0, m, 2):
				dp[0][j] = chr(s + 121)
				dp[0][j + 1] = chr(s + 121)
				s ^= 1
				c += 1
			solve(1, n, m, k, dp, c)
			pri(dp, n, m)
		else:
			print('NO')


def sol(n, m, k):
	if not (k % 2 == 0 and k <= n * (m - m % 2) // 2):
		return None
	a = [[None] * m for i in range(n)]
	z = 0
	for j in range(0, m, 2):
		for i in range(0, n, 2):
			if k >= 2:
				a[i][j] = z
				a[i][j + 1] = z
				a[i + 1][j] = z + 1
				a[i + 1][j + 1] = z + 1
				z += 2
				k -= 2
			else:
				a[i][j] = z
				a[i + 1][j] = z
				z += 1
				if j + 1 < m:
					a[i][j + 1] = z
					a[i + 1][j + 1] = z
					z += 1
	return a

def solve():
	(n, m, k) = map(int, input().split())
	if n % 2 == 0:
		ans = sol(n, m, k)
		if ans is None:
			print('NO')
			return
	else:
		ans = sol(m, n, n * m // 2 - k)
		if ans is None:
			print('NO')
			return
		ans1 = [[None] * m for i in range(n)]
		for i in range(n):
			for j in range(m):
				ans1[i][j] = ans[j][i]
		ans = ans1
	z = 'abcd'
	print('YES')
	for i in range(n):
		v = [None] * m
		for j in range(m):
			v[j] = z[(i // 2 + j // 2) % 2 * 2 + ans[i][j] % 2]
		print(''.join(v))
for i in range(int(input())):
	solve()


def naiveSolve():
	return
chars = 'qwertyuiopasdfghjkl'

def main():

	def getCharHorizontal(i, j):
		taken = set()
		for ii in range(i - 1, i + 2):
			for jj in range(j - 1, j + 3):
				if i == ii and j == jj:
					continue
				if 0 <= ii < n and 0 <= jj < m:
					taken.add(grid[ii][jj])
		for c in chars:
			if c not in taken:
				return c

	def getCharVertical(i, j):
		taken = set()
		for ii in range(i - 1, i + 3):
			for jj in range(j - 1, j + 2):
				if i == ii and j == jj:
					continue
				if 0 <= ii < n and 0 <= jj < m:
					taken.add(grid[ii][jj])
		for c in chars:
			if c not in taken:
				return c
	t = int(input())
	allans = []
	for _ in range(t):
		(n, m, k) = readIntArr()
		grid = [['$' for __ in range(m)] for ___ in range(n)]
		if n * m % 2 == 1:
			allans.append('NO')
			continue
		if n % 2 == 1:
			if m % 2 == 1:
				allans.append('NO')
				continue
			minK = m // 2
			if k < minK:
				allans.append('NO')
				continue
			if (k - minK) % 2 == 1:
				allans.append('NO')
				continue
			allans.append('YES')
			for j in range(0, m, 2):
				grid[n - 1][j] = grid[n - 1][j + 1] = getCharHorizontal(n - 1, j)
			k -= minK
			for j in range(0, m, 2):
				for i in range(n - 1):
					if k > 0:
						grid[i][j] = grid[i][j + 1] = getCharHorizontal(i, j)
						k -= 1
			for i in range(n):
				for j in range(m):
					if grid[i][j] == '$':
						assert i + 1 < n and grid[i + 1][j] == '$'
						grid[i][j] = grid[i + 1][j] = getCharVertical(i, j)
			for row in grid:
				allans.append(''.join(row))
		else:
			if k % 2 == 1:
				allans.append('NO')
				continue
			if m % 2 == 1:
				if k > n * (m - 1) // 2:
					allans.append('NO')
					continue
			allans.append('YES')
			for j in range(0, m - 1, 2):
				for i in range(n):
					if k > 0:
						grid[i][j] = grid[i][j + 1] = getCharHorizontal(i, j)
						k -= 1
			for i in range(n):
				for j in range(m):
					if grid[i][j] == '$':
						assert i + 1 < n and grid[i + 1][j] == '$'
						grid[i][j] = grid[i + 1][j] = getCharVertical(i, j)
			for row in grid:
				allans.append(''.join(row))
	multiLineArrayPrint(allans)
	return
import sys
input = lambda : sys.stdin.readline().rstrip('\r\n')

def oneLineArrayPrint(arr):
	print(' '.join([str(x) for x in arr]))

def multiLineArrayPrint(arr):
	print('\n'.join([str(x) for x in arr]))

def multiLineArrayOfArraysPrint(arr):
	print('\n'.join([' '.join([str(x) for x in y]) for y in arr]))

def readIntArr():
	return [int(x) for x in input().split()]

def makeArr(defaultValFactory, dimensionArr):
	dv = defaultValFactory
	da = dimensionArr
	if len(da) == 1:
		return [dv() for _ in range(da[0])]
	else:
		return [makeArr(dv, da[1:]) for _ in range(da[0])]

def queryInteractive(l, r):
	print('? {} {}'.format(l, r))
	sys.stdout.flush()
	return int(input())

def answerInteractive(x):
	print('! {}'.format(x))
	sys.stdout.flush()
inf = float('inf')
MOD = 998244353
from math import gcd, floor, ceil
for _abc in range(1):
	main()


def paint(n, m):
	matrix = [['' for c in range(m)] for r in range(n)]
	char = [['a', 'b'], ['c', 'd']]
	if n % 2 == 0:
		for r in range(n // 2):
			for c in range(m):
				matrix[2 * r][c] = matrix[2 * r + 1][c] = char[r % 2][c % 2]
	else:
		for r in range(n // 2):
			for c in range(m):
				matrix[2 * r + 1][c] = matrix[2 * r + 2][c] = char[r % 2][c % 2]
	if n % 2 == 0:
		if k % 2 == 1:
			print('NO')
			return
		elif m % 2 == 0:
			print('YES')
		elif n * (m // 2) >= k:
			print('YES')
		else:
			print('NO')
			return
	elif k % 2 == 0 and m // 2 % 2 == 0 and (k >= m // 2):
		print('YES')
	elif k % 2 == 1 and m // 2 % 2 == 1 and (k >= m // 2):
		print('YES')
	else:
		print('NO')
		return
	char = [['e', 'f'], ['g', 'h']]
	painted = 0
	if n % 2 == 0:
		for c in range(m // 2):
			for r in range(n):
				if painted == k:
					return matrix
				matrix[r][2 * c] = matrix[r][2 * c + 1] = char[r % 2][c % 2]
				painted += 1
	else:
		for c in range(m // 2):
			matrix[0][2 * c] = matrix[0][2 * c + 1] = char[0][c % 2]
		painted += m // 2
		for c in range(m // 2):
			for r in range(1, n):
				if painted == k:
					return matrix
				matrix[r][2 * c] = matrix[r][2 * c + 1] = char[r % 2][c % 2]
				painted += 1
	return matrix
t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	matrix = paint(n, m)
	if matrix != None:
		for r in range(n):
			print(''.join(matrix[r]))


from sys import stdin, stdout
import heapq
from collections import defaultdict
import math
import bisect
import io, os

def ncr(n, r, p):
	num = den = 1
	for i in range(r):
		num = num * (n - i) % p
		den = den * (i + 1) % p
	return num * pow(den, p - 2, p) % p

def main():
	t = int(stdin.readline())
	for _ in range(t):
		(n, m, k) = list(map(int, stdin.readline().split()))
		arr = [['a'] * m for _ in range(n)]
		is_ok = True
		if k == 0 and n % 2 == 1:
			is_ok = False
		nn = 0
		mm = 0
		while k > 0:
			if m == 1:
				is_ok = False
				break
			if n % 2 == 1:
				while mm + 2 <= m and k > 0:
					k -= 1
					if mm == 0:
						mm += 2
						continue
					if arr[0][mm - 1] == 'a':
						arr[0][mm] = 'b'
						arr[0][mm + 1] = 'b'
					mm += 2
				if k == 0 and mm < m:
					is_ok = False
					break
				mm = 0
			if k % 2 == 1:
				is_ok = False
				break
			nn = 1 if n % 2 == 1 else 0
			while mm + 2 <= m and k > 0:
				while nn < n and k > 0:
					if (nn + mm // 2) % 2 == 1:
						arr[nn][mm] = 'b'
						arr[nn][mm + 1] = 'b'
					nn += 1
					k -= 1
				if k == 0:
					break
				mm += 2
				nn = 1 if n % 2 == 1 else 0
			if k > 0:
				is_ok = False
				break
		while mm + 2 <= m and is_ok:
			while nn + 2 <= n:
				if nn % 4 < 2:
					arr[nn][mm] = 'c'
					arr[nn + 1][mm] = 'c'
					arr[nn][mm + 1] = 'd'
					arr[nn + 1][mm + 1] = 'd'
				else:
					arr[nn][mm] = 'd'
					arr[nn + 1][mm] = 'd'
					arr[nn][mm + 1] = 'c'
					arr[nn + 1][mm + 1] = 'c'
				nn += 2
			mm += 2
			nn = 1 if n % 2 == 1 else 0
		if is_ok and m % 2 == 1:
			if n % 2 == 1:
				is_ok = False
			else:
				while nn + 2 <= n:
					if nn % 4 < 2:
						arr[nn][mm] = 'c'
						arr[nn + 1][mm] = 'c'
					else:
						arr[nn][mm] = 'd'
						arr[nn + 1][mm] = 'd'
					nn += 2
		if not is_ok:
			stdout.write('NO\n')
			continue
		stdout.write('YES\n')
		for i in range(n):
			for j in range(m):
				stdout.write(arr[i][j])
			stdout.write('\n')
main()


y = 'abcdefghijklmnopqrstuvwxyz'
for i in range(int(input())):
	(n, m, k) = list(map(int, input().split()))
	if n % 2 == 0 and m % 2 == 0:
		z = 'YES' if k % 2 == 0 else 'NO'
		print(z)
		if z == 'YES':
			a = [[' ' for i in range(m)] for j in range(n)]
			for i in range(n // 2):
				for j in range(m // 2):
					if i * (m // 2) + j < k // 2:
						b = 0
						while 2 * i > 0 and (a[2 * i - 1][2 * j] == y[b] or a[2 * i - 1][2 * j + 1] == y[b]) or (2 * j > 0 and a[2 * i][2 * j - 1] == y[b]):
							b += 1
						a[2 * i][2 * j] = y[b]
						a[2 * i][2 * j + 1] = y[b]
						b = 0
						while 2 * i + 1 > 0 and (a[2 * i][2 * j] == y[b] or a[2 * i][2 * j + 1] == y[b]) or (2 * j > 0 and a[2 * i + 1][2 * j - 1] == y[b]):
							b += 1
						a[2 * i + 1][2 * j] = y[b]
						a[2 * i + 1][2 * j + 1] = y[b]
					else:
						b = 0
						while 2 * j > 0 and (a[2 * i][2 * j - 1] == y[b] or a[2 * i + 1][2 * j - 1] == y[b]) or (2 * i > 0 and a[2 * i - 1][2 * j] == y[b]):
							b += 1
						a[2 * i][2 * j] = y[b]
						a[2 * i + 1][2 * j] = y[b]
						b = 0
						while 2 * j + 1 > 0 and (a[2 * i][2 * j] == y[b] or a[2 * i + 1][2 * j] == y[b]) or (2 * i > 0 and a[2 * i - 1][2 * j + 1] == y[b]):
							b += 1
						a[2 * i][2 * j + 1] = y[b]
						a[2 * i + 1][2 * j + 1] = y[b]
			for i in a:
				print(*i, sep='')
	elif m % 2:
		z = 'YES' if k % 2 == 0 and k <= (m - 1) * n // 2 else 'NO'
		print(z)
		if z == 'YES':
			a = [[' ' for i in range(m)] for j in range(n)]
			for i in range(n // 2):
				for j in range(m // 2):
					if i * (m // 2) + j < k // 2:
						b = 0
						while 2 * i > 0 and (a[2 * i - 1][2 * j] == y[b] or a[2 * i - 1][2 * j + 1] == y[b]) or (2 * j > 0 and a[2 * i][2 * j - 1] == y[b]):
							b += 1
						a[2 * i][2 * j] = y[b]
						a[2 * i][2 * j + 1] = y[b]
						b = 0
						while 2 * i + 1 > 0 and (a[2 * i][2 * j] == y[b] or a[2 * i][2 * j + 1] == y[b]) or (2 * j > 0 and a[2 * i + 1][2 * j - 1] == y[b]):
							b += 1
						a[2 * i + 1][2 * j] = y[b]
						a[2 * i + 1][2 * j + 1] = y[b]
					else:
						b = 0
						while 2 * j > 0 and (a[2 * i][2 * j - 1] == y[b] or a[2 * i + 1][2 * j - 1] == y[b]) or (2 * i > 0 and a[2 * i - 1][2 * j] == y[b]):
							b += 1
						a[2 * i][2 * j] = y[b]
						a[2 * i + 1][2 * j] = y[b]
						b = 0
						while 2 * j + 1 > 0 and (a[2 * i][2 * j] == y[b] or a[2 * i + 1][2 * j] == y[b]) or (2 * i > 0 and a[2 * i - 1][2 * j + 1] == y[b]):
							b += 1
						a[2 * i][2 * j + 1] = y[b]
						a[2 * i + 1][2 * j + 1] = y[b]
			for i in range(n // 2):
				b = 0
				while m > 1 and (a[2 * i][m - 2] == y[b] or a[2 * i + 1][m - 2] == y[b]) or (i > 0 and a[2 * i - 1][m - 1] == y[b]):
					b += 1
				a[2 * i][m - 1] = y[b]
				a[2 * i + 1][m - 1] = y[b]
			for i in a:
				print(*i, sep='')
	elif m % 4 == 0:
		z = 'YES' if k % 2 == 0 and k >= m // 2 else 'NO'
		print(z)
		if z == 'YES':
			a = [[' ' for i in range(m)] for j in range(n)]
			for i in range(m // 2):
				b = 0
				while i > 0 and a[0][2 * i - 1] == y[b]:
					b += 1
				a[0][2 * i] = y[b]
				a[0][2 * i + 1] = y[b]
			k -= m // 2
			for i in range(n // 2):
				for j in range(m // 2):
					if i * (m // 2) + j < k // 2:
						b = 0
						while 2 * i + 1 > 0 and (a[2 * i][2 * j] == y[b] or a[2 * i][2 * j + 1] == y[b]) or (2 * j > 0 and a[2 * i + 1][2 * j - 1] == y[b]):
							b += 1
						a[2 * i + 1][2 * j] = y[b]
						a[2 * i + 1][2 * j + 1] = y[b]
						b = 0
						while 2 * i + 2 > 0 and (a[2 * i + 1][2 * j] == y[b] or a[2 * i + 1][2 * j + 1] == y[b]) or (2 * j > 0 and a[2 * i + 2][2 * j - 1] == y[b]):
							b += 1
						a[2 * i + 2][2 * j] = y[b]
						a[2 * i + 2][2 * j + 1] = y[b]
					else:
						b = 0
						while 2 * j > 0 and (a[2 * i + 1][2 * j - 1] == y[b] or a[2 * i + 2][2 * j - 1] == y[b]) or (2 * i + 1 > 0 and a[2 * i][2 * j] == y[b]):
							b += 1
						a[2 * i + 1][2 * j] = y[b]
						a[2 * i + 2][2 * j] = y[b]
						b = 0
						while 2 * j + 1 > 0 and (a[2 * i + 1][2 * j] == y[b] or a[2 * i + 2][2 * j] == y[b]) or (2 * i + 1 > 0 and a[2 * i][2 * j + 1] == y[b]):
							b += 1
						a[2 * i + 1][2 * j + 1] = y[b]
						a[2 * i + 2][2 * j + 1] = y[b]
			for i in a:
				print(*i, sep='')
	else:
		z = 'YES' if k % 2 == 1 and k >= m // 2 else 'NO'
		print(z)
		if z == 'YES':
			a = [[' ' for i in range(m)] for j in range(n)]
			for i in range(m // 2):
				b = 0
				while i > 0 and a[0][2 * i - 1] == y[b]:
					b += 1
				a[0][2 * i] = y[b]
				a[0][2 * i + 1] = y[b]
			k -= m // 2
			for i in range(n // 2):
				for j in range(m // 2):
					if i * (m // 2) + j < k // 2:
						b = 0
						while 2 * i + 1 > 0 and (a[2 * i][2 * j] == y[b] or a[2 * i][2 * j + 1] == y[b]) or (2 * j > 0 and a[2 * i + 1][2 * j - 1] == y[b]):
							b += 1
						a[2 * i + 1][2 * j] = y[b]
						a[2 * i + 1][2 * j + 1] = y[b]
						b = 0
						while 2 * i + 2 > 0 and (a[2 * i + 1][2 * j] == y[b] or a[2 * i + 1][2 * j + 1] == y[b]) or (2 * j > 0 and a[2 * i + 2][2 * j - 1] == y[b]):
							b += 1
						a[2 * i + 2][2 * j] = y[b]
						a[2 * i + 2][2 * j + 1] = y[b]
					else:
						b = 0
						while 2 * j > 0 and (a[2 * i + 1][2 * j - 1] == y[b] or a[2 * i + 2][2 * j - 1] == y[b]) or (2 * i + 1 > 0 and a[2 * i][2 * j] == y[b]):
							b += 1
						a[2 * i + 1][2 * j] = y[b]
						a[2 * i + 2][2 * j] = y[b]
						b = 0
						while 2 * j + 1 > 0 and (a[2 * i + 1][2 * j] == y[b] or a[2 * i + 2][2 * j] == y[b]) or (2 * i + 1 > 0 and a[2 * i][2 * j + 1] == y[b]):
							b += 1
						a[2 * i + 1][2 * j + 1] = y[b]
						a[2 * i + 2][2 * j + 1] = y[b]
			for i in a:
				print(*i, sep='')


import os, sys
from io import BytesIO, IOBase

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, 8192))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, 8192))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
inp = lambda dtype: dtype(input().strip())
inp_d = lambda dtype: [dtype(x) for x in input().split()]
inp_2d = lambda dtype, n: [inp(dtype) for _ in range(n)]
inp_2ds = lambda dtype, n: [inp_d(dtype) for _ in range(n)]
inp_enu = lambda dtype: [(i, x) for (i, x) in enumerate(inp_d(dtype))]
inp_enus = lambda dtype, n: [[i, inp_d(dtype)] for i in range(n)]
ceil1 = lambda a, b: (a + b - 1) // b
valid = lambda x, y: -1 < x < r and -1 < y < c
(dx, dy) = ((0, 1, 0, -1, 1, -1, 1, -1), (1, 0, -1, 0, 1, -1, -1, 1))

def build_ver():
	global ver
	for i in range(1, r):
		for j in range(c):
			if not ver:
				return
			if not (out[i][j] or out[i - 1][j]):
				(neighbor, ver) = ([], ver - 1)
				for k in range(4):
					(x, y, x1) = (dx[k] + i, dy[k] + j, dx[k] + i - 1)
					if valid(x, y):
						neighbor.append(out[x][y])
					if valid(x1, y):
						neighbor.append(out[x1][y])
				for k in range(26):
					ch = chr(97 + k)
					if ch not in neighbor:
						out[i][j] = out[i - 1][j] = ch
						break

def build_hor():
	global hor
	for j in range(1, c):
		for i in range(r):
			if not hor:
				return
			if not (out[i][j] or out[i][j - 1]):
				(neighbor, hor) = ([], hor - 1)
				for k in range(4):
					(x, y, y1) = (dx[k] + i, dy[k] + j, dy[k] + j - 1)
					if valid(x, y):
						neighbor.append(out[x][y])
					if valid(x, y1):
						neighbor.append(out[x][y1])
				for k in range(26):
					ch = chr(97 + k)
					if ch not in neighbor:
						out[i][j] = out[i][j - 1] = ch
						break
for _ in range(inp(int)):
	(r, c, hor) = inp_d(int)
	all = r * c // 2
	(ver, ans) = (all - hor, 0)
	if r & 1:
		ans = ver & 1 or ver > (r - 1) * c // 2
	elif c & 1:
		ans = hor & 1 or hor > r * (c - 1) // 2
	else:
		ans = hor & 1
	if ans:
		print('NO')
	else:
		print('YES')
		out = [[''] * c for _ in range(r)]
		if r & 1:
			build_ver()
			build_hor()
		else:
			build_hor()
			build_ver()
		[print(*x, sep='') for x in out]


t = int(input())
abc = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
set_abc = set(abc)

def color_hor(i, j, n, m, construct):
	cols = set()
	if j - 1 >= 0:
		cols.add(construct[i][j - 1])
	if j + 2 < m:
		cols.add(construct[i][j + 2])
	if i - 1 >= 0:
		cols.add(construct[i - 1][j])
		cols.add(construct[i - 1][j])
	if i + 1 < n:
		cols.add(construct[i + 1][j])
		cols.add(construct[i + 1][j])
	c = set_abc.difference(cols)
	color = c.pop()
	return color

def color_ver(i, j, n, m, construct):
	cols = set()
	if j - 1 >= 0:
		cols.add(construct[i][j - 1])
		cols.add(construct[i + 1][j - 1])
	if j + 1 < m:
		cols.add(construct[i][j + 1])
		cols.add(construct[i + 1][j + 1])
	if i - 1 >= 0:
		cols.add(construct[i - 1][j])
	if i + 2 < n:
		cols.add(construct[i + 2][j])
	c = set_abc.difference(cols)
	color = c.pop()
	return color

def solve():
	(n, m, k) = map(int, input().split())
	construct = [['' for _ in range(m)] for _ in range(n)]
	if n % 2 == 0:
		if k % 2 == 1:
			print('NO')
			return
		if m % 2 == 0:
			print('YES')
			is_k = True
			for i in range(0, n, 2):
				for j in range(0, m, 2):
					if k == 0:
						is_k = False
					if is_k:
						color = color_hor(i, j, n, m, construct)
						construct[i][j] = color
						construct[i][j + 1] = color
						color = color_hor(i + 1, j, n, m, construct)
						construct[i + 1][j] = color
						construct[i + 1][j + 1] = color
						k -= 2
					else:
						color = color_ver(i, j, n, m, construct)
						construct[i][j] = color
						construct[i + 1][j] = color
						color = color_ver(i, j + 1, n, m, construct)
						construct[i][j + 1] = color
						construct[i + 1][j + 1] = color
			for row in construct:
				print(''.join(row))
			return
		if k > (m - 1) * n / 2:
			print('NO')
		else:
			print('YES')
			for i in range(0, n, 2):
				color = color_ver(i, 0, n, m, construct)
				construct[i][0] = color
				construct[i + 1][0] = color
			color = 0
			for i in range(0, n, 2):
				construct[i][0] = abc[color]
				construct[i + 1][0] = abc[color]
				color = (color + 1) % 26
			is_k = True
			for i in range(0, n, 2):
				for j in range(1, m, 2):
					if k == 0:
						is_k = False
					if is_k:
						color = color_hor(i, j, n, m, construct)
						construct[i][j] = color
						construct[i][j + 1] = color
						color = color_hor(i + 1, j, n, m, construct)
						construct[i + 1][j] = color
						construct[i + 1][j + 1] = color
						k -= 2
					else:
						color = color_ver(i, j, n, m, construct)
						construct[i][j] = color
						construct[i + 1][j] = color
						color = color_ver(i, j + 1, n, m, construct)
						construct[i][j + 1] = color
						construct[i + 1][j + 1] = color
			for row in construct:
				print(''.join(row))
		return
	l = m // 2
	if k < l:
		print('NO')
		return
	if (k - l) % 2 == 0:
		print('YES')
		color = 0
		for i in range(0, m, 2):
			construct[0][i] = abc[color]
			construct[0][i + 1] = abc[color]
			color = (color + 1) % 26
		k -= l
		is_k = True
		for i in range(1, n, 2):
			for j in range(0, m, 2):
				if k == 0:
					is_k = False
				if is_k:
					color = color_hor(i, j, n, m, construct)
					construct[i][j] = color
					construct[i][j + 1] = color
					color = color_hor(i + 1, j, n, m, construct)
					construct[i + 1][j] = color
					construct[i + 1][j + 1] = color
					k -= 2
				else:
					color = color_ver(i, j, n, m, construct)
					construct[i][j] = color
					construct[i + 1][j] = color
					color = color_ver(i, j + 1, n, m, construct)
					construct[i][j + 1] = color
					construct[i + 1][j + 1] = color
		for row in construct:
			print(''.join(row))
	else:
		print('NO')
for _ in range(t):
	solve()


import sys
pl = 1
sys.setrecursionlimit(10 ** 5)
if pl:
	input = sys.stdin.readline
else:
	sys.stdin = open('input.txt', 'r')
	sys.stdout = open('outpt.txt', 'w')

def li():
	return [int(xxx) for xxx in input().split()]

def fi():
	return int(input())

def si():
	return list(input().rstrip())

def mi():
	return map(int, input().split())

def ff():
	sys.stdout.flush()

def google(tc, *ans):
	print('Case #' + str(tc) + ':', *ans)
t = fi()
f = t

def check(i, j, k):
	for u in range(-1, 2):
		for v in range(-1, 2):
			if abs(u) + abs(v) == 1 and 0 <= i + u < n and (0 <= j + v < m) and (ans[i + u][j + v] == chr(k + ord('a'))):
				return False
	return True

def process(ans, flag=0):
	for i in range(n):
		for j in range(m):
			if ans[i][j] == 'h':
				for k in range(26):
					if chr(k + ord('a')) not in ['v', 'h'] and check(i, j, k) and check(i, j + 1, k):
						ans[i][j] = ans[i][j + 1] = chr(k + ord('a'))
						break
			elif ans[i][j] == 'v':
				for k in range(26):
					if chr(k + ord('a')) not in ['v', 'h'] and check(i, j, k) and check(i + 1, j, k):
						ans[i][j] = ans[i + 1][j] = chr(k + ord('a'))
						break
	if flag == 0:
		for i in range(n):
			for j in range(m):
				print(ans[i][j], end='')
			print()
	else:
		for i in range(m):
			for j in range(n):
				print(ans[j][i], end='')
			print()
while t > 0:
	t -= 1
	(n, m, k) = mi()
	p = n * m // 2
	ans = [['v'] * m for i in range(n)]
	if n % 2 == 0 and m % 2 == 0:
		print('YES' if k % 2 == 0 else 'NO')
		if k % 2 == 0:
			p = n
			i = 0
			while i < m // 2 and p > 0 and (k > 0):
				if k >= p:
					for j in range(p):
						ans[j][2 * i] = ans[j][2 * i + 1] = 'h'
					i += 1
					k -= p
				else:
					p -= 2
			process(ans)
	elif n == 1:
		print('YES' if k == p else 'NO')
		if k == p:
			ans[0] = ['h'] * m
			process(ans)
	elif m == 1:
		print('YES' if k == 0 else 'NO')
		if k == 0:
			process(ans)
	elif n % 2:
		k -= m // 2
		print('YES' if k % 2 == 0 and k >= 0 else 'NO')
		p = n - 1
		ans[0] = ['h'] * m
		if k % 2 == 0 and k >= 0:
			i = 0
			while i < m // 2 and p > 0 and (k > 0):
				if k >= p:
					for j in range(1, p + 1):
						ans[j][2 * i] = ans[j][2 * i + 1] = 'h'
					i += 1
					k -= p
				else:
					p -= 2
			process(ans)
	else:
		k = p - k
		(n, m) = (m, n)
		k -= m // 2
		p = n - 1
		ans = [['v'] * m for i in range(n)]
		ans[0] = ['h'] * m
		print('YES' if k % 2 == 0 and k >= 0 else 'NO')
		if k % 2 == 0 and k >= 0:
			i = 0
			while i < m // 2 and p > 0 and (k > 0):
				if k >= p:
					for j in range(1, p + 1):
						ans[j][2 * i] = ans[j][2 * i + 1] = 'h'
					i += 1
					k -= p
				else:
					p -= 2
			process(ans, 1)


t = int(input())
h1 = 'ac'
h2 = 'bd'
s1 = 'ef'
s2 = 'gh'
for aslkfjalkfj in range(t):
	(n, m, k) = [int(i) for i in input().split()]
	kk = n * m // 2 - k
	if n % 2 and m % 2:
		print('NO')
		continue
	elif n % 2:
		k -= m // 2
	elif m % 2:
		kk -= n / 2
	if k < 0 or k % 2 or kk < 0:
		print('NO')
		continue
	print('YES')
	mp = [''] * n
	x = 0
	y = 0
	tmp = 0
	if n % 2:
		while k > 0:
			mp[y] += h1[tmp] + h1[tmp]
			mp[y + 1] += h2[tmp] + h2[tmp]
			tmp = 1 - tmp
			x += 2
			k -= 2
			if x == m:
				x = 0
				y += 2
		while kk > 0:
			if y > 0:
				if mp[y - 1][x] == s1[tmp]:
					tmp = 1 - tmp
			mp[y] += s1[tmp] + s2[tmp]
			mp[y + 1] += s1[tmp] + s2[tmp]
			tmp = 1 - tmp
			x += 2
			kk -= 2
			if x == m:
				x = 0
				y += 2
		mp[n - 1] = 'xxyy' * (m // 4) + 'x' * (m % 4)
	if m % 2:
		while k > 0:
			mp[y] += h1[tmp] + h1[tmp]
			mp[y + 1] += h2[tmp] + h2[tmp]
			tmp = 1 - tmp
			x += 2
			k -= 2
			if x == m - 1:
				x = 0
				y += 2
		while kk > 0:
			if y > 0:
				if mp[y - 1][x] == s1[tmp]:
					tmp = 1 - tmp
			mp[y] += s1[tmp] + s2[tmp]
			mp[y + 1] += s1[tmp] + s2[tmp]
			tmp = 1 - tmp
			x += 2
			kk -= 2
			if x == m - 1:
				x = 0
				y += 2
		x = 'xy'
		for i in range(0, n, 2):
			mp[i] += x[tmp]
			mp[i + 1] += x[tmp]
			tmp = 1 - tmp
	else:
		while k > 0:
			mp[y] += h1[tmp] + h1[tmp]
			mp[y + 1] += h2[tmp] + h2[tmp]
			tmp = 1 - tmp
			x += 2
			k -= 2
			if x == m:
				x = 0
				y += 2
		while kk > 0:
			if y > 0:
				if mp[y - 1][x] == s1[tmp]:
					tmp = 1 - tmp
			mp[y] += s1[tmp] + s2[tmp]
			mp[y + 1] += s1[tmp] + s2[tmp]
			tmp = 1 - tmp
			x += 2
			kk -= 2
			if x == m:
				x = 0
				y += 2
	for i in mp:
		print(i)


import os
import sys
from io import BytesIO, IOBase
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
from math import ceil

def prod(a, mod=10 ** 9 + 7):
	ans = 1
	for each in a:
		ans = ans * each % mod
	return ans

def gcd(x, y):
	while y:
		(x, y) = (y, x % y)
	return x

def lcm(a, b):
	return a * b // gcd(a, b)

def binary(x, length=16):
	y = bin(x)[2:]
	return y if len(y) >= length else '0' * (length - len(y)) + y
for _ in range(int(input()) if True else 1):
	(n, m, k) = map(int, input().split())

	def solve(n, m, k, invert=False):
		ans = [[''] * m for _ in range(n)]
		(i, j) = (0, 0)
		while k:
			k -= 1
			ans[i][j] = ans[i][j + 1] = ['ab'[j % 4 == 0], 'cd'[j % 4 == 0]][i % 2]
			i = (i + 1) % n
			if i == 0:
				j += 2
		if i:
			for x in range(i, n, 2):
				ans[x][j] = ans[x + 1][j] = ['ef'[x % 4 == 0], 'gh'[x % 4 == 0]][j % 2]
				ans[x][j + 1] = ans[x + 1][j + 1] = ['ef'[x % 4 == 0], 'gh'[x % 4 == 0]][(j + 1) % 2]
			j += 2
		if j != m:
			for x in range(j, m):
				for y in range(0, n, 2):
					ans[y][x] = ans[y + 1][x] = ['ef'[y % 4 == 0], 'gh'[y % 4 == 0]][x % 2]
		if invert:
			ans = zip(*ans)
		for row in ans:
			print(*row, sep='')
	if n % 2 == m % 2 == 0:
		if k % 2:
			print('NO')
		else:
			print('YES')
			solve(n, m, k)
	elif n % 2 == 0:
		if k % 2 or k > n * (m // 2):
			print('NO')
		else:
			print('YES')
			solve(n, m, k)
	else:
		k2 = n * m // 2 - k
		if k2 % 2 or k2 > m * (n // 2):
			print('NO')
		else:
			print('YES')
			solve(m, n, k2, True)


import sys
input = sys.stdin.readline
from collections import Counter, defaultdict
for _ in range(int(input())):
	(n, m, k) = map(int, input().split())
	if not n % 2:
		if not k % 2:
			if k > m // 2 * n:
				print('NO')
			else:
				print('YES')
				ans = [[''] * m for _ in range(n)]
				(x, y) = divmod(k, n)
				for i in range(x):
					for j in range(n):
						if not i % 2:
							if not j % 2:
								ans[j][i * 2] = 'a'
								ans[j][i * 2 + 1] = 'a'
							else:
								ans[j][i * 2] = 'b'
								ans[j][i * 2 + 1] = 'b'
						elif not j % 2:
							ans[j][i * 2] = 'b'
							ans[j][i * 2 + 1] = 'b'
						else:
							ans[j][i * 2] = 'a'
							ans[j][i * 2 + 1] = 'a'
				if y:
					i = x
					for j in range(y):
						if not i % 2:
							if not j % 2:
								ans[j][i * 2] = 'a'
								ans[j][i * 2 + 1] = 'a'
							else:
								ans[j][i * 2] = 'b'
								ans[j][i * 2 + 1] = 'b'
						elif not j % 2:
							ans[j][i * 2] = 'b'
							ans[j][i * 2 + 1] = 'b'
						else:
							ans[j][i * 2] = 'a'
							ans[j][i * 2 + 1] = 'a'
				for i in range(n):
					for j in range(m):
						if ans[i][j]:
							continue
						if not j % 2:
							if i // 2 % 2:
								ans[i][j] = 'c'
							else:
								ans[i][j] = 'd'
						elif i // 2 % 2:
							ans[i][j] = 'd'
						else:
							ans[i][j] = 'c'
				for a in ans:
					print(''.join(a))
		else:
			print('NO')
	elif k < m // 2:
		print('NO')
	else:
		k -= m // 2
		ans = [[''] * m for _ in range(n)]
		for j in range(m):
			if j // 2 % 2:
				ans[-1][j] = 'e'
			else:
				ans[-1][j] = 'f'
		if not k % 2:
			if k > m // 2 * n:
				print('NO')
			else:
				print('YES')
				n -= 1
				if n:
					(x, y) = divmod(k, n)
					for i in range(x):
						for j in range(n):
							if not i % 2:
								if not j % 2:
									ans[j][i * 2] = 'a'
									ans[j][i * 2 + 1] = 'a'
								else:
									ans[j][i * 2] = 'b'
									ans[j][i * 2 + 1] = 'b'
							elif not j % 2:
								ans[j][i * 2] = 'b'
								ans[j][i * 2 + 1] = 'b'
							else:
								ans[j][i * 2] = 'a'
								ans[j][i * 2 + 1] = 'a'
					if y:
						i = x
						for j in range(y):
							if not i % 2:
								if not j % 2:
									ans[j][i * 2] = 'a'
									ans[j][i * 2 + 1] = 'a'
								else:
									ans[j][i * 2] = 'b'
									ans[j][i * 2 + 1] = 'b'
							elif not j % 2:
								ans[j][i * 2] = 'b'
								ans[j][i * 2 + 1] = 'b'
							else:
								ans[j][i * 2] = 'a'
								ans[j][i * 2 + 1] = 'a'
					for i in range(n):
						for j in range(m):
							if ans[i][j]:
								continue
							if not j % 2:
								if i // 2 % 2:
									ans[i][j] = 'c'
								else:
									ans[i][j] = 'd'
							elif i // 2 % 2:
								ans[i][j] = 'd'
							else:
								ans[i][j] = 'c'
				for a in ans:
					print(''.join(a))
		else:
			print('NO')


def put(field, x1, y1, x2, y2):
	left = {'a', 'b', 'c', 'd', 'e', 'f', 'g'}
	if x1 > 0:
		left.discard(field[y1][x1 - 1])
	if x2 > 0:
		left.discard(field[y2][x2 - 1])
	if y1 > 0:
		left.discard(field[y1 - 1][x1])
	if y2 > 0:
		left.discard(field[y2 - 1][x2])
	if x1 < len(field[0]) - 1:
		left.discard(field[y1][x1 + 1])
	if x2 < len(field[0]) - 1:
		left.discard(field[y2][x2 + 1])
	if y1 < len(field) - 1:
		left.discard(field[y1 + 1][x1])
	if y2 < len(field) - 1:
		left.discard(field[y2 + 1][x2])
	field[y1][x1] = left.pop()
	field[y2][x2] = field[y1][x1]

def fill_even(n, m, k):
	field = [[0 for x in range(m)] for y in range(n)]
	for y0 in range(n // 2):
		for x0 in range(m // 2):
			if k > 0:
				put(field, 2 * x0, 2 * y0, 2 * x0 + 1, 2 * y0)
				put(field, 2 * x0, 2 * y0 + 1, 2 * x0 + 1, 2 * y0 + 1)
				k -= 2
			else:
				put(field, 2 * x0, 2 * y0, 2 * x0, 2 * y0 + 1)
				put(field, 2 * x0 + 1, 2 * y0, 2 * x0 + 1, 2 * y0 + 1)
	return field

def fill_odd(n, m, k):
	field = fill_even(n - 1, m, k - m // 2)
	field.append([0 for x in range(m)])
	for x in range(m // 2):
		put(field, 2 * x, n - 1, 2 * x + 1, n - 1)
	return field

def print_out(field):
	print('\n'.join([''.join(x) for x in field]))
t = int(input())
for XXX in range(t):
	(n, m, k) = map(int, input().split())
	if n % 2 == 0:
		if m % 2 == 0:
			if k % 2 == 1:
				print('NO')
			else:
				print('YES')
				print_out(fill_even(n, m, k))
		elif n * m // 2 - k < n // 2 or (n * m // 2 - k - n // 2) % 2 != 0:
			print('NO')
		else:
			print('YES')
			field = fill_odd(m, n, n * m // 2 - k)
			ans = [[0 for x in range(m)] for y in range(n)]
			for i in range(n):
				for j in range(m):
					ans[i][j] = field[j][i]
			print_out(ans)
	elif k < m // 2 or (k - m // 2) % 2 != 0:
		print('NO')
	else:
		print('YES')
		print_out(fill_odd(n, m, k))


import io, os
input = io.BytesIO(os.read(0, os.fstat(0).st_size)).readline
direc = [[0, -1], [0, 1], [1, 0], [-1, 0]]
alphabet = 'abcdefghijklmnopqrstuvwxyz'

def getsurround(ans, i1, j1, i2, j2, m, n):
	dic = {}
	for d in range(4):
		newi = i1 + direc[d][0]
		newj = j1 + direc[d][1]
		if newi < 0 or newi >= m or newj < 0 or (newj >= n):
			continue
		if ans[newi][newj] == '#':
			continue
		dic[ans[newi][newj]] = 1
	for d in range(4):
		newi = i2 + direc[d][0]
		newj = j2 + direc[d][1]
		if newi < 0 or newi >= m or newj < 0 or (newj >= n):
			continue
		if ans[newi][newj] == '#':
			continue
		dic[ans[newi][newj]] = 1
	return dic

def getnext(ans, rest, i, j, m, n):
	for ii in range(i, m, 2):
		for jj in range(j, n, 2):
			if rest > 0:
				dic = getsurround(ans, ii, jj, ii, jj + 1, m, n)
				for c in alphabet:
					if c not in dic:
						ans[ii][jj] = c
						ans[ii][jj + 1] = c
						break
				dic = getsurround(ans, ii + 1, jj, ii + 1, jj + 1, m, n)
				for c in alphabet:
					if c not in dic:
						ans[ii + 1][jj] = c
						ans[ii + 1][jj + 1] = c
						break
				rest -= 2
			else:
				dic = getsurround(ans, ii, jj, ii + 1, jj, m, n)
				for c in alphabet:
					if c not in dic:
						ans[ii][jj] = c
						ans[ii + 1][jj] = c
						break
				dic = getsurround(ans, ii, jj + 1, ii + 1, jj + 1, m, n)
				for c in alphabet:
					if c not in dic:
						ans[ii][jj + 1] = c
						ans[ii + 1][jj + 1] = c
						break
	return ans

def main(t):
	(m, n, k) = map(int, input().split())
	flag = False
	if m % 2 == 1:
		if (m * n // 2 - k) % 2 == 0 and k >= n // 2:
			flag = True
	elif n % 2 == 1:
		if k % 2 == 0 and m * n // 2 - k >= m // 2:
			flag = True
	elif k % 2 == 0:
		flag = True
	if not flag:
		print('NO')
		return
	print('YES')
	ans = [['#' for j in range(n)] for i in range(m)]
	rest = k
	if m % 2 == 1:
		for j in range(0, n, 2):
			ans[0][j] = chr(j % 26 + 97)
			ans[0][j + 1] = chr(j % 26 + 97)
			rest -= 1
		ans = getnext(ans, rest, 1, 0, m, n)
	elif n % 2 == 1:
		for i in range(0, m, 2):
			ans[i][0] = chr(i % 26 + 97)
			ans[i + 1][0] = chr(i % 26 + 97)
		ans = getnext(ans, rest, 0, 1, m, n)
	else:
		ans = getnext(ans, rest, 0, 0, m, n)
	for e in ans:
		print(''.join(e))
T = int(input())
t = 1
while t <= T:
	main(t)
	t += 1


import sys
input = sys.stdin.readline

def f(x, y, n, m):
	a = [0 for i in range(26)]
	dx = [-1, 0, 0, 1]
	dy = [0, -1, 1, 0]
	for i in range(4):
		if x + dx[i] < n and x + dx[i] >= 0 and (y + dy[i] >= 0) and (y + dy[i] < m):
			a[ans[x + dx[i]][y + dy[i]]] += 1
	for i in range(4):
		if x + dx[i] < n and x + dx[i] >= 0 and (y + dy[i] + 1 >= 0) and (y + dy[i] + 1 < m):
			a[ans[x + dx[i]][y + dy[i] + 1]] += 1
	for i in range(1, 26):
		if a[i] == 0:
			return i

def g(x, y, n, m):
	a = [0 for i in range(26)]
	dx = [-1, 0, 0, 1]
	dy = [0, -1, 1, 0]
	for i in range(4):
		if x + dx[i] < n and x + dx[i] >= 0 and (y + dy[i] >= 0) and (y + dy[i] < m):
			a[ans[x + dx[i]][y + dy[i]]] += 1
	for i in range(4):
		if x + dx[i] + 1 < n and x + dx[i] + 1 >= 0 and (y + dy[i] >= 0) and (y + dy[i] < m):
			a[ans[x + dx[i] + 1][y + dy[i]]] += 1
	for i in range(1, 26):
		if a[i] == 0:
			return i
t = int(input())
for you in range(t):
	l = input().split()
	n = int(l[0])
	m = int(l[1])
	k = int(l[2])
	if m % 2:
		if k % 2 == 0 and k <= (m - 1) // 2 * n:
			print('YES')
			ans = [[0 for i in range(m)] for i in range(n)]
			curr = 0
			for j in range(m):
				for i in range(n):
					if curr >= k:
						break
					if ans[i][j] != 0:
						continue
					ans[i][j] = f(i, j, n, m)
					ans[i][j + 1] = ans[i][j]
					ans[i + 1][j] = f(i + 1, j, n, m)
					ans[i + 1][j + 1] = ans[i + 1][j]
					curr += 2
			for i in range(n):
				for j in range(m):
					if ans[i][j] != 0:
						continue
					ans[i][j] = g(i, j, n, m)
					ans[i + 1][j] = ans[i][j]
			for i in ans:
				for j in i:
					print(chr(ord('a') + j), end='')
				print()
		else:
			print('NO')
		continue
	if n % 2:
		z = m * n // 2
		z -= k
		if z % 2 == 0 and k >= m // 2:
			print('YES')
			k = z
			(n, m) = (m, n)
			ans = [[0 for i in range(m)] for i in range(n)]
			curr = 0
			for j in range(m):
				for i in range(n):
					if curr >= k:
						break
					if ans[i][j] != 0:
						continue
					ans[i][j] = f(i, j, n, m)
					ans[i][j + 1] = ans[i][j]
					ans[i + 1][j] = f(i + 1, j, n, m)
					ans[i + 1][j + 1] = ans[i + 1][j]
					curr += 2
			for i in range(n):
				for j in range(m):
					if ans[i][j] != 0:
						continue
					ans[i][j] = g(i, j, n, m)
					ans[i + 1][j] = ans[i][j]
			for i in range(m):
				for j in range(n):
					print(chr(ord('a') + ans[j][i]), end='')
				print()
		else:
			print('NO')
		continue
	if k % 2:
		print('NO')
	else:
		print('YES')
		ans = [[0 for i in range(m)] for i in range(n)]
		curr = 0
		for j in range(m):
			for i in range(n):
				if curr >= k:
					break
				if ans[i][j] != 0:
					continue
				ans[i][j] = f(i, j, n, m)
				ans[i][j + 1] = ans[i][j]
				ans[i + 1][j] = f(i + 1, j, n, m)
				ans[i + 1][j + 1] = ans[i + 1][j]
				curr += 2
		for i in range(n):
			for j in range(m):
				if ans[i][j] != 0:
					continue
				ans[i][j] = g(i, j, n, m)
				ans[i + 1][j] = ans[i][j]
		for i in ans:
			for j in i:
				print(chr(ord('a') + j), end='')
			print()


import sys
import math
import random
from queue import PriorityQueue as PQ
from bisect import bisect_left as BSL
from bisect import bisect_right as BSR
from collections import OrderedDict as OD
from collections import Counter
from itertools import permutations
mod = 1000000007
sys.setrecursionlimit(1000000)
try:
	sys.stdin = open('actext.txt', 'r')
	OPENFILE = 1
except:
	pass

def get_ints():
	return map(int, input().split())

def palindrome(s):
	mid = len(s) // 2
	for i in range(mid):
		if s[i] != s[len(s) - i - 1]:
			return False
	return True

def check(i, n):
	if 0 <= i < n:
		return True
	else:
		return False

def check(i, j, n, m):
	if 0 <= i < n and 0 <= j < m:
		return True
	else:
		return False

def choose_char(i1, j1, n, m, mat):
	chars = 'abcdefghijklmnopqrstuvwxyz0'
	charmap = {i: False for i in chars}
	xx = [-2, -1, 0, 1, 2, -2, -1, 0, 1, 2, -2, -1, 0, 1, 2, -2, -1, 0, 1, 2, -2, -1, 0, 1, 2]
	yy = [-2, -2, -2, -2, -2, -1, -1, -1, -1, -1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2]
	for i in range(25):
		x1 = i1 + xx[i]
		y1 = j1 + yy[i]
		if check(x1, y1, n, m):
			charmap[mat[x1][y1]] = True
	for (i, j) in charmap.items():
		if not j:
			return i

def fill_mat_row(sx, sy, n, m, k, mat):
	flg = 0
	for i in range(sx, n, 2):
		for j in range(sy, m, 2):
			if k == 0:
				flg = 1
				break
			cch = choose_char(i, j, n, m, mat)
			mat[i][j] = cch
			mat[i][j + 1] = cch
			cch = choose_char(i + 1, j, n, m, mat)
			mat[i + 1][j] = cch
			mat[i + 1][j + 1] = cch
			k -= 2
		if flg == 1:
			break
t = int(input())
for tt in range(t):
	(n, m, k) = get_ints()
	ans = 0
	mat = [[0 for i in range(m)] for j in range(n)]
	if n % 2 != 0 and m % 2 != 0:
		print('NO')
	elif n % 2 == 0 and m % 2 == 0:
		mi = 0
		mx = n * m // 2
		if mi <= k <= mx and k % 2 == 0:
			print('YES')
			ans = 1
			fill_mat_row(0, 0, n, m, k, mat)
		else:
			print('NO')
	elif n % 2 == 0:
		mi = 0
		mx = n * (m // 2)
		if mi <= k <= mx and k % 2 == 0:
			print('YES')
			ans = 1
			fill_mat_row(0, 0, n, m - 1, k, mat)
		else:
			print('NO')
	else:
		mi = m // 2
		mx = n * m // 2
		if mi <= k <= mx:
			k = k - mi
			if k % 2 == 0:
				print('YES')
				for i in range(0, m, 2):
					cch = choose_char(0, i, n, m, mat)
					mat[0][i] = cch
					mat[0][i + 1] = cch
				ans = 1
				fill_mat_row(1, 0, n, m, k, mat)
			else:
				print('NO')
		else:
			print('NO')
	if ans == 1:
		for i in range(n):
			for j in range(m):
				if mat[i][j] == 0:
					cch = choose_char(i, j, n, m, mat)
					mat[i][j] = cch
					mat[i + 1][j] = cch
		for i in range(n):
			print(''.join(mat[i]))


import sys, os
from io import BytesIO, IOBase
mod = 10 ** 9 + 7
Mod = 998244353
INF = float('inf')
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
inp = lambda : list(map(int, sys.stdin.readline().rstrip('\r\n').split()))
from collections import defaultdict as dd
from collections import Counter as cc
tc = 1
tc = int(input())
for test in range(1, tc + 1):
	(n, m, k) = inp()
	f = False

	def solve(n, m, comp, ans):
		lol1 = False
		lol2 = False
		for i in range(n // 2):
			a = []
			b = []
			Char = ord('a')
			if lol1:
				Char += 4
			for j in range(m // 2):
				if lol2:
					Char += 2
				ch1 = chr(Char)
				ch2 = chr(Char + 1)
				if comp:
					a.extend([ch1, ch1])
					b.extend([ch2, ch2])
					comp -= 2
				else:
					a.extend([ch1, ch2])
					b.extend([ch1, ch2])
				if lol2:
					Char -= 2
				lol2 = not lol2
			if lol1:
				Char -= 4
			lol1 = not lol1
			ans.append(a[:])
			ans.append(b[:])
	if n & 1:
		comp = k - m // 2
		if comp >= 0 and comp & 1 == 0:
			f = True
			ans = []
			a = []
			for i in range(m // 2):
				ch = chr(ord('x') + i % 2)
				a.extend([ch, ch])
			ans.append(a[:])
			solve(n, m, comp, ans)
	elif m & 1:
		tot = m // 2 * n
		if k <= tot and k % 2 == 0:
			f = True
			(n, m) = (m, n)
			comp = n * m // 2 - k - m // 2
			ans = []
			a = []
			for i in range(m // 2):
				ch = chr(ord('x') + i % 2)
				a.extend([ch, ch])
			ans.append(a[:])
			solve(n, m, comp, ans)
			act = [['0'] * n for i in range(m)]
			for i in range(m):
				for j in range(n):
					act[i][j] = ans[j][i]
			ans = act
	elif k % 2 == 0:
		f = True
		ans = []
		lol = False
		comp = k
		solve(n, m, comp, ans)
	if f:
		print('YES')
		for i in ans:
			print(*i, sep='')
	else:
		print('NO')


import random
from collections import *

def name(a):

	def adj_names(a, y, x, ancs=None):
		was_empty = False
		if ancs is None:
			was_empty = True
			ancs = set()
		if (y, x) in ancs:
			return set()
		ancs.add((y, x))
		res = set()
		try:
			n = a[y + 1][x]
			if n is None:
				return None
			if type(n) == str:
				res.add(n)
			if was_empty:
				res.update(adj_names(a, y + 1, x, ancs))
		except BaseException:
			pass
		if y > 0:
			n = a[y - 1][x]
			if n is None:
				return None
			if type(n) == str:
				res.add(n)
			if was_empty:
				res.update(adj_names(a, y - 1, x, ancs))
		try:
			n = a[y][x + 1]
			if n is None:
				return None
			if type(n) == str:
				res.add(n)
			if was_empty:
				res.update(adj_names(a, y, x + 1, ancs))
		except BaseException:
			pass
		if x > 0:
			n = a[y][x - 1]
			if n is None:
				return None
			if type(n) == str:
				res.add(n)
			if was_empty:
				res.update(adj_names(a, y, x - 1, ancs))
		return res

	def set_name(a, y, x, s):
		c = a[y][x]
		try:
			if c == a[y][x + 1]:
				a[y][x] = a[y][x + 1] = s
				return
		except BaseException:
			pass
		if x > 0 and c == a[y][x - 1]:
			a[y][x] = a[y][x - 1] = s
			return
		try:
			if a[y + 1][x] == c:
				a[y + 1][x] = a[y][x] = s
				return
		except BaseException:
			pass
		if y > 0 and c == a[y - 1][x]:
			a[y][x] = a[y - 1][x] = s
			return
	n = len(a)
	m = len(a[0])
	for i in range(n):
		for j in range(m):
			c = a[i][j]
			if c is None:
				return 'NO'
			if type(c) == str:
				continue
			adj = adj_names(a, i, j)
			if adj is None:
				return 'NO'
			while True:
				c = random.choice([chr(i) for i in range(ord('a'), ord('a') + 26)])
				if c not in adj:
					set_name(a, i, j, c)
					break
	return a

def solve(n, m, k):
	ans = [[None for _ in range(m)] for _ in range(n)]
	c = 0
	if n % 2 != 0:
		for j in range(0, m, 2):
			if c == k:
				break
			ans[0][j] = ans[0][j + 1] = c
			c += 1
	for j in range(0, m - m % 2, 2):
		for i in range(n):
			if ans[i][j] is not None:
				continue
			if c == k:
				break
			ans[i][j] = ans[i][j + 1] = c
			c += 1
	t = n * m // 2 - k
	p = 0
	for j in range(m - 1, -1, -1):
		if p == t:
			break
		for i in range(n - 1, -1, -2):
			if p == t:
				break
			if ans[i][j] is not None or ans[i - 1][j] is not None:
				continue
			ans[i][j] = ans[i - 1][j] = c
			c += 1
			p += 1
	return name(ans)
random.seed(0)
t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	if n * m % 2 != 0:
		print('NO')
		continue
	ans = solve(n, m, k)
	if ans == 'NO':
		print('NO')
		continue
	print('YES')
	for line in ans:
		print(*line, sep='')


oa = ord('a')

def slv(n, m, k):
	ans = [[-1] * m for i in range(n)]
	if k & 1:
		return None
	if k > m // 2 * n:
		return None
	cnt = 0
	for i in range(0, n, 2):
		for j in range(0, m - 1, 2):
			hh = i // 2 % 2 * 2 + j // 2 % 2
			c1 = 2 * hh
			c2 = 2 * hh + 1
			if cnt == k:
				ans[i][j] = c1
				ans[i + 1][j] = c1
				ans[i][j + 1] = c2
				ans[i + 1][j + 1] = c2
			else:
				ans[i][j] = c1
				ans[i][j + 1] = c1
				ans[i + 1][j] = c2
				ans[i + 1][j + 1] = c2
				cnt += 2
	if m & 1:
		for j in range(0, n, 2):
			c = 8 if j & 2 else 9
			ans[j][m - 1] = c
			ans[j + 1][m - 1] = c
	return ans
for _ in range(int(input())):
	(n, m, k) = [int(i) for i in input().split()]
	ans = []
	if n & 1:
		if k >= m // 2:
			ans = slv(n - 1, m, k - m // 2)
			if ans is None:
				print('NO')
				continue
			lst = [-1] * m
			for i in range(0, m, 2):
				c = 10 if i & 2 else 11
				lst[i] = c
				lst[i + 1] = c
			ans.append(lst)
		else:
			print('NO')
			continue
	else:
		ans = slv(n, m, k)
		if ans is None:
			print('NO')
			continue
	print('YES')
	for rw in ans:
		print(''.join((chr(p + oa) for p in rw)))


for input_number in range(int(input())):
	(n, m, k) = map(int, input().split())
	a = []
	for i in range(n):
		a.append([])
		for j in range(m):
			a[i].append('0')
	if n % 2 == 1:
		if k - m // 2 >= 0 and (k - m // 2) % 2 == 0:
			print('YES')
			c = 0
			for i in range((k - m // 2) // 2):
				a[i // (m // 2) * 2][i % (m // 2) * 2] = chr(ord('a') + c)
				a[i // (m // 2) * 2][i % (m // 2) * 2 + 1] = chr(ord('a') + c)
				a[i // (m // 2) * 2 + 1][i % (m // 2) * 2] = chr(ord('a') + (c + 1) % 4)
				a[i // (m // 2) * 2 + 1][i % (m // 2) * 2 + 1] = chr(ord('a') + (c + 1) % 4)
				c = (c + 2) % 4
			c = 0
			for i in range((k - m // 2) // 2, (n - 1) * m // 2 // 2):
				a[i // (m // 2) * 2][i % (m // 2) * 2] = chr(ord('e') + c)
				a[i // (m // 2) * 2][i % (m // 2) * 2 + 1] = chr(ord('e') + (c + 1) % 4)
				a[i // (m // 2) * 2 + 1][i % (m // 2) * 2] = chr(ord('e') + c)
				a[i // (m // 2) * 2 + 1][i % (m // 2) * 2 + 1] = chr(ord('e') + (c + 1) % 4)
				if (i + 1) % (m // 2) == 0:
					c = (c + 1) % 4
				c = (c + 2) % 4
			c = 0
			for i in range(m // 2):
				a[n - 1][i * 2] = chr(ord('s') + c)
				a[n - 1][i * 2 + 1] = chr(ord('s') + c)
				c = (c + 1) % 2
			for i in range(n):
				print(''.join(a[i]))
		else:
			print('NO')
	elif m % 2 == 1:
		if n * m / 2 - k - n // 2 >= 0 and (n * m / 2 - k - n // 2) % 2 == 0:
			print('YES')
			c = 0
			for i in range(k // 2):
				a[i // (m // 2) * 2][i % (m // 2) * 2] = chr(ord('a') + c)
				a[i // (m // 2) * 2][i % (m // 2) * 2 + 1] = chr(ord('a') + c)
				a[i // (m // 2) * 2 + 1][i % (m // 2) * 2] = chr(ord('a') + (c + 1) % 4)
				a[i // (m // 2) * 2 + 1][i % (m // 2) * 2 + 1] = chr(ord('a') + (c + 1) % 4)
				c = (c + 2) % 4
			c = 0
			for i in range(k // 2, n * (m - 1) // 2 // 2):
				a[i // (m // 2) * 2][i % (m // 2) * 2] = chr(ord('e') + c)
				a[i // (m // 2) * 2][i % (m // 2) * 2 + 1] = chr(ord('e') + (c + 1) % 4)
				a[i // (m // 2) * 2 + 1][i % (m // 2) * 2] = chr(ord('e') + c)
				a[i // (m // 2) * 2 + 1][i % (m // 2) * 2 + 1] = chr(ord('e') + (c + 1) % 4)
				if (i + 1) % ((m - 1) // 2) == 0:
					c = (c + 1) % 4
				c = (c + 2) % 4
			c = 0
			for i in range(n // 2):
				a[i * 2][m - 1] = chr(ord('x') + c)
				a[i * 2 + 1][m - 1] = chr(ord('x') + c)
				c = (c + 1) % 2
			for i in range(n):
				print(''.join(a[i]))
		else:
			print('NO')
	elif k % 2 == 0:
		print('YES')
		c = 0
		for i in range(k // 2):
			a[i // (m // 2) * 2][i % (m // 2) * 2] = chr(ord('a') + c)
			a[i // (m // 2) * 2][i % (m // 2) * 2 + 1] = chr(ord('a') + c)
			a[i // (m // 2) * 2 + 1][i % (m // 2) * 2] = chr(ord('a') + (c + 1) % 4)
			a[i // (m // 2) * 2 + 1][i % (m // 2) * 2 + 1] = chr(ord('a') + (c + 1) % 4)
			c = (c + 2) % 4
		c = 0
		for i in range(k // 2, n * m // 2 // 2):
			a[i // (m // 2) * 2][i % (m // 2) * 2] = chr(ord('e') + c)
			a[i // (m // 2) * 2][i % (m // 2) * 2 + 1] = chr(ord('e') + (c + 1) % 4)
			a[i // (m // 2) * 2 + 1][i % (m // 2) * 2] = chr(ord('e') + c)
			a[i // (m // 2) * 2 + 1][i % (m // 2) * 2 + 1] = chr(ord('e') + (c + 1) % 4)
			if (i + 1) % (m // 2) == 0:
				c = (c + 1) % 4
			c = (c + 2) % 4
		for i in range(n):
			print(''.join(a[i]))
	else:
		print('NO')


T = int(input())
for _ in range(T):
	(N, M, K) = map(int, input().split())
	ans = [['_'] * M for _ in range(N)]
	dxy = [(0, 1), (1, 0), (0, -1), (-1, 0)]
	if N % 2 == 0 and M % 2 == 0:
		if K % 2 == 0:
			print('YES')
			for i in range(N // 2):
				for j in range(M // 2):
					if K > 0:
						K -= 2
						ns = set()
						(x, y) = (j * 2, i * 2)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						x += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y][x - 1] = c
								break
						ns = set()
						(x, y) = (j * 2, i * 2 + 1)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						x += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y][x - 1] = c
								break
					else:
						ns = set()
						(x, y) = (j * 2, i * 2)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						y += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y - 1][x] = c
								break
						ns = set()
						(x, y) = (j * 2 + 1, i * 2)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						y += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y - 1][x] = c
								break
		else:
			print('NO')
			continue
	elif N % 2 == 0 and M % 2:
		l = N * M // 2 - K
		if K % 2 == 0 and l * 2 >= N:
			print('YES')
			for y in range(N):
				c = 'y' if y % 4 < 2 else 'z'
				ans[y][-1] = c
			for i in range(N // 2):
				for j in range(M // 2):
					if K > 0:
						K -= 2
						ns = set()
						(x, y) = (j * 2, i * 2)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						x += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y][x - 1] = c
								break
						ns = set()
						(x, y) = (j * 2, i * 2 + 1)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						x += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y][x - 1] = c
								break
					else:
						ns = set()
						(x, y) = (j * 2, i * 2)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						y += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y - 1][x] = c
								break
						ns = set()
						(x, y) = (j * 2 + 1, i * 2)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						y += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y - 1][x] = c
								break
		else:
			print('NO')
			continue
	else:
		l = N * M // 2 - K
		if l % 2 == 0 and K * 2 >= M:
			print('YES')
			for x in range(M):
				c = 'y' if x % 4 < 2 else 'z'
				ans[-1][x] = c
			K -= M // 2
			for i in range(N // 2):
				for j in range(M // 2):
					if K > 0:
						K -= 2
						ns = set()
						(x, y) = (j * 2, i * 2)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						x += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y][x - 1] = c
								break
						ns = set()
						(x, y) = (j * 2, i * 2 + 1)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						x += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y][x - 1] = c
								break
					else:
						ns = set()
						(x, y) = (j * 2, i * 2)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						y += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y - 1][x] = c
								break
						ns = set()
						(x, y) = (j * 2 + 1, i * 2)
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						y += 1
						for (dx, dy) in dxy:
							(nx, ny) = (x + dx, y + dy)
							if not 0 <= nx < M:
								continue
							if not 0 <= ny < N:
								continue
							ns.add((nx, ny))
						for ci in range(26):
							c = chr(ord('a') + ci)
							for (nx, ny) in ns:
								if ans[ny][nx] == c:
									break
							else:
								ans[y][x] = c
								ans[y - 1][x] = c
								break
		else:
			print('NO')
			continue
	for row in ans:
		print(''.join(row))


import sys
import io
import math
import collections
import decimal
import itertools
import bisect
import heapq

def input():
	return sys.stdin.readline()[:-1]
INF = 10 ** 10
YES = 'YES'
NO = 'NO'

def place(N, M, Map):
	T = [[''] * M for _ in range(N)]
	D1 = 'ab'
	q = []
	if Map[0][0]:
		T[0][0] = D1[0]
		T[0][1] = D1[0]
		q.append((0, 0, 0))
	while q:
		(i, j, c) = q.pop()
		if i + 1 < N and Map[i + 1][j] and (T[i + 1][j] == ''):
			T[i + 1][j] = D1[1 - c]
			T[i + 1][j + 1] = D1[1 - c]
			q.append((i + 1, j, 1 - c))
		if j + 3 < M and Map[i][j + 2] and (T[i][j + 2] == ''):
			T[i][j + 2] = D1[1 - c]
			T[i][j + 3] = D1[1 - c]
			q.append((i, j + 2, 1 - c))
	D2 = 'cd'
	q = []
	if not T[N - 1][M - 1]:
		T[N - 2][M - 1] = D2[0]
		T[N - 1][M - 1] = D2[0]
		q.append((N - 1, M - 1, 0))
	while q:
		(i, j, c) = q.pop()
		if i - 3 >= 0 and (not Map[i - 2][j]) and (T[i - 2][j] == ''):
			T[i - 3][j] = D2[1 - c]
			T[i - 2][j] = D2[1 - c]
			q.append((i - 2, j, 1 - c))
		if j - 1 >= 0 and (not Map[i][j - 1]) and (T[i][j - 1] == ''):
			T[i - 1][j - 1] = D2[1 - c]
			T[i][j - 1] = D2[1 - c]
			q.append((i, j - 1, 1 - c))
	return [''.join(T[i]) for i in range(N)]

def solve(N, M, K):
	Map = [[False] * M for _ in range(N)]
	if N % 2 == 0:
		if K % N % 2 == 0 and math.ceil(K / N) * 2 <= M:
			(i, j) = (0, 0)
			for k in range(K):
				Map[i][j] = True
				Map[i][j + 1] = True
				i += 1
				if i == N:
					i = 0
					j += 2
			return ['YES', place(N, M, Map)]
	else:
		if M % 2 == 1:
			return ['NO']
		if M // 2 % 2 == 0:
			if K >= M // 2 and K % 2 == 0:
				for k in range(M // 2):
					Map[0][k * 2] = True
					Map[0][k * 2 + 1] = True
				(i, j) = (1, 0)
				k = M // 2
				while k < K:
					Map[i][j] = True
					Map[i][j + 1] = True
					Map[i + 1][j] = True
					Map[i + 1][j + 1] = True
					k += 2
					i += 2
					if i == N:
						i = 1
						j += 2
				return ['YES', place(N, M, Map)]
		elif K >= M // 2 and K % 2 == 1:
			for k in range(M // 2):
				Map[0][k * 2] = True
				Map[0][k * 2 + 1] = True
			(i, j) = (1, 0)
			k = M // 2
			while k < K:
				Map[i][j] = True
				Map[i][j + 1] = True
				Map[i + 1][j] = True
				Map[i + 1][j + 1] = True
				k += 2
				i += 2
				if i == N:
					i = 1
					j += 2
			return ['YES', place(N, M, Map)]
	return ['NO']
T0 = int(input())
for _ in range(T0):
	(N, M, K) = map(int, input().split())
	ans = solve(N, M, K)
	if len(ans) == 1:
		print(ans[0])
	else:
		print(ans[0])
		for i in range(N):
			print(ans[1][i])


t = int(input())
for test_idx in range(1, t + 1):
	(n, m, k) = map(int, input().split(' '))
	nk = k
	if n % 2:
		delta = m // 2
		k -= delta
		nk -= delta
		if k < 0:
			print('NO')
		elif k % 2:
			print('NO')
		else:
			print('YES')
			res = [['z'] * m for __ in range(n)]
			for i in range(n // 2):
				for j in range(m // 2):
					if nk:
						if j % 2:
							res[2 * i][2 * j] = 'c'
							res[2 * i][2 * j + 1] = 'c'
							res[2 * i + 1][2 * j] = 'd'
							res[2 * i + 1][2 * j + 1] = 'd'
						else:
							res[2 * i][2 * j] = 'd'
							res[2 * i][2 * j + 1] = 'd'
							res[2 * i + 1][2 * j] = 'c'
							res[2 * i + 1][2 * j + 1] = 'c'
						nk -= 2
					elif i % 2:
						res[2 * i][2 * j] = 'a'
						res[2 * i][2 * j + 1] = 'b'
						res[2 * i + 1][2 * j] = 'a'
						res[2 * i + 1][2 * j + 1] = 'b'
					else:
						res[2 * i][2 * j] = 'b'
						res[2 * i][2 * j + 1] = 'a'
						res[2 * i + 1][2 * j] = 'b'
						res[2 * i + 1][2 * j + 1] = 'a'
			for j in range(m // 2):
				if j % 2:
					res[-1][2 * j] = 'z'
					res[-1][2 * j + 1] = 'z'
				else:
					res[-1][2 * j] = 'y'
					res[-1][2 * j + 1] = 'y'
			for c in res:
				print(''.join(c))
	elif m % 2:
		if k % 2:
			print('NO')
		elif 2 * k > n * (m - 1):
			print('NO')
		else:
			print('YES')
			res = [['z'] * m for __ in range(n)]
			for i in range(n // 2):
				for j in range(m // 2):
					if nk:
						if j % 2:
							res[2 * i][2 * j] = 'c'
							res[2 * i][2 * j + 1] = 'c'
							res[2 * i + 1][2 * j] = 'd'
							res[2 * i + 1][2 * j + 1] = 'd'
						else:
							res[2 * i][2 * j] = 'd'
							res[2 * i][2 * j + 1] = 'd'
							res[2 * i + 1][2 * j] = 'c'
							res[2 * i + 1][2 * j + 1] = 'c'
						nk -= 2
					elif i % 2:
						res[2 * i][2 * j] = 'a'
						res[2 * i][2 * j + 1] = 'b'
						res[2 * i + 1][2 * j] = 'a'
						res[2 * i + 1][2 * j + 1] = 'b'
					else:
						res[2 * i][2 * j] = 'b'
						res[2 * i][2 * j + 1] = 'a'
						res[2 * i + 1][2 * j] = 'b'
						res[2 * i + 1][2 * j + 1] = 'a'
			for i in range(n // 2):
				if i % 2:
					res[2 * i][-1] = 'z'
					res[2 * i + 1][-1] = 'z'
				else:
					res[2 * i][-1] = 'y'
					res[2 * i + 1][-1] = 'y'
			for c in res:
				print(''.join(c))
	elif k % 2:
		print('NO')
	else:
		print('YES')
		res = [['z'] * m for __ in range(n)]
		for i in range(n // 2):
			for j in range(m // 2):
				if nk:
					if j % 2:
						res[2 * i][2 * j] = 'c'
						res[2 * i][2 * j + 1] = 'c'
						res[2 * i + 1][2 * j] = 'd'
						res[2 * i + 1][2 * j + 1] = 'd'
					else:
						res[2 * i][2 * j] = 'd'
						res[2 * i][2 * j + 1] = 'd'
						res[2 * i + 1][2 * j] = 'c'
						res[2 * i + 1][2 * j + 1] = 'c'
					nk -= 2
				elif i % 2:
					res[2 * i][2 * j] = 'a'
					res[2 * i][2 * j + 1] = 'b'
					res[2 * i + 1][2 * j] = 'a'
					res[2 * i + 1][2 * j + 1] = 'b'
				else:
					res[2 * i][2 * j] = 'b'
					res[2 * i][2 * j + 1] = 'a'
					res[2 * i + 1][2 * j] = 'b'
					res[2 * i + 1][2 * j + 1] = 'a'
		for c in res:
			print(''.join(c))


def build_board_1(n, m, k):
	board = [[''] * m for i in range(n)]
	current_row = 0
	current_index = 0
	k //= 2
	for i in range(k):
		if current_index >= m - 1:
			current_row += 2
			current_index = 0
		if current_index % 4 == 2:
			board[current_row][current_index] = 'a'
			board[current_row][current_index + 1] = 'a'
			board[current_row + 1][current_index] = 'b'
			board[current_row + 1][current_index + 1] = 'b'
		else:
			board[current_row][current_index] = 'e'
			board[current_row][current_index + 1] = 'e'
			board[current_row + 1][current_index] = 'f'
			board[current_row + 1][current_index + 1] = 'f'
		current_index += 2
	vertical = n * m // 2 - 2 * k
	vertical //= 2
	for i in range(vertical):
		if current_index >= m - 1:
			current_row += 2
			current_index = 0
		if current_row % 4 == 2:
			board[current_row][current_index] = 'c'
			board[current_row + 1][current_index] = 'c'
			board[current_row][current_index + 1] = 'd'
			board[current_row + 1][current_index + 1] = 'd'
		else:
			board[current_row][current_index] = 'g'
			board[current_row + 1][current_index] = 'g'
			board[current_row][current_index + 1] = 'h'
			board[current_row + 1][current_index + 1] = 'h'
		current_index += 2
	return [''.join(row) for row in board]
t = int(input())
results = []
for i in range(t):
	(n, m, k) = map(int, input().split())
	if n % 2 == 0 and m % 2 == 0:
		if k % 2 == 0:
			results.append(('YES', '\n'.join(build_board_1(n, m, k))))
		else:
			results.append('NO')
	elif n % 2 == 0 and m % 2 == 1:
		if k % 2 == 0 and n * (m - 1) >= 2 * k:
			rows = build_board_1(n, m - 1, k)
			for j in range(0, len(rows), 2):
				if j % 4 == 2:
					rows[j] += 'x'
					rows[j + 1] += 'x'
				else:
					rows[j] += 'z'
					rows[j + 1] += 'z'
			results.append(('YES', '\n'.join(rows)))
		else:
			results.append('NO')
	elif n % 2 == 1 and m % 2 == 0:
		if 2 * k < m:
			results.append('NO')
		else:
			k = k - m // 2
			if k % 2 == 0:
				rows = build_board_1(n - 1, m, k)
				new_row = ''
				for j in range(m // 2):
					if j % 2 == 0:
						new_row += 'ii'
					else:
						new_row += 'jj'
				rows = [new_row] + rows
				results.append(('YES', '\n'.join(rows)))
			else:
				results.append('NO')
for i in range(t):
	if results[i] == 'NO':
		print(results[i])
	else:
		print(results[i][0])
		print(results[i][1])


direcs = [(0, 1), (0, -1), (1, 0), (-1, 0)]

def populate(idx_1, idx_2):
	colors = set(['a', 'b', 'c', 'd', 'e', 'f', 'g'])
	for direc in direcs:
		new_idx = (idx_1[0] + direc[0], idx_1[1] + direc[1])
		if 0 <= new_idx[0] < m and 0 <= new_idx[1] < n:
			if final_mat[new_idx[0]][new_idx[1]] in colors:
				colors.remove(final_mat[new_idx[0]][new_idx[1]])
		new_idx = (idx_2[0] + direc[0], idx_2[1] + direc[1])
		if 0 <= new_idx[0] < m and 0 <= new_idx[1] < n:
			if final_mat[new_idx[0]][new_idx[1]] in colors:
				colors.remove(final_mat[new_idx[0]][new_idx[1]])
	color = list(colors)[0]
	final_mat[idx_1[0]][idx_1[1]] = color
	final_mat[idx_2[0]][idx_2[1]] = color
t = int(input())
for i in range(1, t + 1):
	(m, n, k_h) = list(map(int, input().split()))
	k_v = m * n // 2 - k_h
	if n == 1 and k_h > 0 or (m == 1 and k_v > 0):
		print('NO')
	else:
		final_mat = [[None for _ in range(n)] for _ in range(m)]
		to_print = False
		if n % 2 == 0:
			curr_row = 0
			if m % 2 == 1:
				k_h -= n // 2
				for idx in range(0, n, 2):
					populate((0, idx), (0, idx + 1))
				curr_row += 1
			if k_h < 0 or k_h % 2 == 1:
				print('NO')
			else:
				print('YES')
				to_print = True
				start_row = curr_row
				curr_m = start_row
				curr_n = 0
				while k_h > 0:
					k_h -= 1
					populate((curr_m, curr_n + 0), (curr_m, curr_n + 1))
					curr_m += 1
					if curr_m == m:
						curr_m = start_row
						curr_n += 2
				if curr_m != start_row:
					while curr_m < m - 1:
						populate((curr_m, curr_n), (curr_m + 1, curr_n))
						populate((curr_m, curr_n + 1), (curr_m + 1, curr_n + 1))
						curr_m += 2
						k_v -= 2
					curr_n += 2
					curr_m = start_row
				while k_v > 0:
					k_v -= 1
					populate((curr_m, curr_n), (curr_m + 1, curr_n))
					curr_m += 2
					if curr_m >= m:
						curr_m = start_row
						curr_n += 1
		else:
			curr_col = 0
			if n % 2 == 1:
				k_v -= m // 2
				for idx in range(0, m, 2):
					populate((idx, 0), (idx + 1, 0))
				curr_col += 1
			if k_v < 0 or k_v % 2 == 1:
				print('NO')
			else:
				print('YES')
				to_print = True
				start_col = curr_col
				curr_m = 0
				curr_n = start_col
				while k_v > 0:
					k_v -= 1
					populate((curr_m, curr_n), (curr_m + 1, curr_n))
					curr_n += 1
					if curr_n == n:
						curr_n = start_col
						curr_m += 2
				if curr_n != start_col:
					while curr_n < n - 1:
						populate((curr_m, curr_n), (curr_m, curr_n + 1))
						populate((curr_m + 1, curr_n), (curr_m + 1, curr_n + 1))
						curr_n += 2
						k_h -= 2
					curr_m += 2
					curr_n = start_col
				while k_h > 0:
					k_h -= 1
					populate((curr_m, curr_n), (curr_m, curr_n + 1))
					curr_n += 2
					if curr_n >= n:
						curr_n = start_col
						curr_m += 1
		if to_print:
			for row in final_mat:
				print(''.join(row))


fin = 0
strs = 'abcdefghijklmnopqrstuvwxyz'
idx = 0

def YESNO(flg):
	global fin
	if not fin:
		print('YES' if flg else 'NO')
	if not flg:
		fin = 1

def solve(N, M, A, B):
	global idx
	global strs

	def fillhor(i, j):
		global answer
		assert 0 <= i < N and 0 <= j < M - 1
		answer[i][j] = '<'
		answer[i][j + 1] = '>'

	def fillver(i, j):
		global answer
		assert 0 <= i < N - 1 and 0 <= j < M
		answer[i][j] = '^'
		answer[i + 1][j] = 'v'
	if N % 2 == M % 2 == 0:
		square_num = (A + 1) // 2 + (B + 1) // 2
		if N * M // 4 < square_num:
			YESNO(False)
		else:
			YESNO(True)
			for i in range(0, N, 2):
				for j in range(0, M, 2):
					if A:
						fillhor(i, j)
						A -= 1
						if A:
							fillhor(i + 1, j)
							A -= 1
					elif B:
						fillver(i, j)
						B -= 1
						if B:
							fillver(i, j + 1)
							B -= 1
	elif N % 2 == 0 and M % 2 == 1:
		j = M - 1
		for i in range(0, N, 2):
			if B:
				fillver(i, j)
				B -= 1
		solve(N, M - 1, A, B)
	elif N % 2 == 1 and M % 2 == 0:
		i = N - 1
		for j in range(0, M, 2):
			if A:
				fillhor(i, j)
				A -= 1
		solve(N - 1, M, A, B)
	elif N == 1 and M == 1:
		YESNO(A == 0 and B == 0)
	elif N == 1 and M != 1:
		YESNO(2 * A <= M and B == 0)
		for i in range(0, M, 2):
			if A:
				fillhor(0, i)
				A -= 1
	elif N != 1 and M == 1:
		YESNO(2 * B <= N and A == 0)
		for i in range(0, N, 2):
			if B:
				fillver(i, 0)
				B -= 1
	else:
		j = M - 1
		for i in range(0, N - 1, 2):
			if B:
				fillver(i, j)
				B -= 1
		if B % 2 == 1:
			fillver(N - 2, M - 3)
			B -= 1
			if A:
				fillhor(N - 3, M - 3)
				A -= 1
			if A:
				fillhor(N - 1, M - 2)
				A -= 1
		else:
			if A:
				fillhor(N - 1, M - 3)
				A -= 1
			if B >= 2:
				fillver(N - 3, M - 3)
				fillver(N - 3, M - 2)
				B -= 2
			else:
				if A:
					fillhor(N - 3, M - 3)
					A -= 1
				if A:
					fillhor(N - 2, M - 3)
					A -= 1
		j = M - 3
		for i in range(0, N - 3, 2):
			if B:
				fillver(i, j)
				B -= 1
				if B:
					fillver(i, j + 1)
					B -= 1
			elif A:
				fillhor(i, j)
				A -= 1
				if A:
					fillhor(i + 1, j)
					A -= 1
		if M > 3:
			solve(N, M - 3, A, B)
		else:
			YESNO(A == 0 and B == 0)
t = int(input())
for _ in range(t):
	fin = 0
	idx = 0
	(N, M, A) = map(int, input().split())
	B = N * M // 2 - A
	answer = [['.'] * M for _ in range(N)]
	answer2 = [['.'] * M for _ in range(N)]
	solve(N, M, A, B)
	if not fin:
		for i in range(N):
			for j in range(M):
				if answer[i][j] == '<':
					while strs[idx] == answer2[i - 1][j] or (j + 1 < M and strs[idx] == answer2[i - 1][j + 1]) or (j - 1 >= 0 and strs[idx] == answer2[i][j - 1]) or (j + 2 < M and strs[idx] == answer2[i - 1][j + 2]):
						idx += 1
						idx %= 26
					answer2[i][j] = answer2[i][j + 1] = strs[idx]
				elif answer[i][j] == '^':
					while strs[idx] == answer2[i - 1][j] or (j + 1 < M and strs[idx] == answer2[i][j + 1]) or (j - 1 >= 0 and strs[idx] == answer2[i][j - 1]):
						idx += 1
						idx %= 26
					answer2[i][j] = answer2[i + 1][j] = strs[idx]
		for row in answer2:
			print(''.join(row))


dh = [['cc', 'dd', 'ee', 'ff'], ['gg', 'hh', 'ii', 'jj']]
dv = [['kl', 'mn'], ['op', 'qr']]
d1 = 'ab'
tt = int(input())
for _ in range(tt):
	(n, m, k) = map(int, input().split())
	minh = m // 2 if n % 2 else 0
	minv = n // 2 if m % 2 else 0
	if k >= minh and (k - minh) % 2 == 0 and (k - minh <= n * m // 2 - minv):
		print('YES')
		for j in range(minh):
			print('aa' if j % 2 else 'bb', end='')
		if n % 2:
			print()
		r = (k - minh) // 2
		for i in range(n // 2):
			if m % 2:
				print(d1[i % 2], end='')
			f = min(r, m // 2)
			r -= f
			for j in range(f):
				print(dh[i % 2][i % 2 * 2 + j % 2], end='')
			for j in range(f, m // 2):
				print(dv[i % 2][j % 2], end='')
			print()
			if m % 2:
				print(d1[i % 2], end='')
			for j in range(f):
				print(dh[i % 2][(i + 1) % 2 * 2 + j % 2], end='')
			for j in range(f, m // 2):
				print(dv[i % 2][j % 2], end='')
			print()
	else:
		print('NO')


from copy import deepcopy
t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	c = 0
	ans = []
	for i in range(0, n, 2):
		temp = []
		for j in range(0, m):
			if len(ans) and ans[-1][j] == chr(c + ord('a')):
				c += 1
				c %= 26
			temp.append(chr(c + ord('a')))
			c += 1
			c %= 26
		ans.append(deepcopy(temp))
		if i != n - 1:
			ans.append(temp)

	def valid(i, j, c):
		if i != 0 and ans[i - 1][j] == c:
			return False
		if i != n - 1 and ans[i + 1][j] == c:
			return False
		if j != 0 and ans[i][j - 1] == c:
			return False
		if j != m - 1 and ans[i][j + 1] == c:
			return False
		return True
	if n % 2 == 0 and m % 2 == 0:
		if k % 2 == 0:
			print('YES')
			i = 0
			j = 0
			while k != 0:
				k -= 2
				while not (valid(i, j, chr(c + ord('a'))) and valid(i, j + 1, chr(c + ord('a')))):
					c += 1
					c %= 26
				ans[i][j] = ans[i][j + 1] = chr(c + ord('a'))
				c += 1
				c %= 26
				while not (valid(i + 1, j, chr(c + ord('a'))) and valid(i + 1, j + 1, chr(c + ord('a')))):
					c += 1
					c %= 26
				ans[i + 1][j] = ans[i + 1][j + 1] = chr(c + ord('a'))
				c += 1
				c %= 26
				i += 2
				if i == n:
					i = 0
					j += 2
			for i in range(n):
				print(''.join(ans[i]))
		else:
			print('NO')
	elif n % 2 == 0 and m % 2 == 1:
		if k % 2 == 0 and k <= n * (m - 1) // 2:
			print('YES')
			i = 0
			j = 0
			while k != 0:
				k -= 2
				while not (valid(i, j, chr(c + ord('a'))) and valid(i, j + 1, chr(c + ord('a')))):
					c += 1
					c %= 26
				ans[i][j] = ans[i][j + 1] = chr(c + ord('a'))
				c += 26
				c %= 26
				while not (valid(i + 1, j, chr(c + ord('a'))) and valid(i + 1, j + 1, chr(c + ord('a')))):
					c += 1
					c %= 26
				ans[i + 1][j] = ans[i + 1][j + 1] = chr(c + ord('a'))
				c += 1
				c %= 26
				i += 2
				if i == n:
					i = 0
					j += 2
			for i in range(n):
				print(''.join(ans[i]))
		else:
			print('NO')
	elif n % 2 == 1 and m % 2 == 0:
		if k >= m // 2 and (k - m // 2) % 2 == 0:
			print('YES')
			for i in range(0, m, 2):
				while not (valid(n - 1, i, chr(c + ord('a'))) and valid(n - 1, i + 1, chr(c + ord('a')))):
					c += 1
					c %= 26
				ans[n - 1][i] = ans[n - 1][i + 1] = chr(c + ord('a'))
				c += 1
				c %= 26
			i = 0
			j = 0
			k -= m // 2
			while k != 0:
				k -= 2
				while not (valid(i, j, chr(c + ord('a'))) and valid(i, j + 1, chr(c + ord('a')))):
					c += 1
					c %= 26
				ans[i][j] = ans[i][j + 1] = chr(c + ord('a'))
				c += 1
				c %= 26
				while not (valid(i + 1, j, chr(c + ord('a'))) and valid(i + 1, j + 1, chr(c + ord('a')))):
					c += 1
					c %= 26
				ans[i + 1][j] = ans[i + 1][j + 1] = chr(c + ord('a'))
				c += 1
				c %= 26
				i += 2
				if i == n - 1:
					i = 0
					j += 2
			for i in range(n):
				print(''.join(ans[i]))
		else:
			print('NO')


import sys
input = sys.stdin.readline
al3 = list('abcdefghijklmnopqrstuvwx')
al2 = ['y', 'z']
t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	yoko = k
	tate = n * m // 2 - k
	ans = [[0] * (m + 5) for i in range(n + 5)]
	(N, M) = (n, m)
	if n % 2 == 1:
		if yoko < m // 2:
			print('NO')
			continue
		else:
			now = 0
			for i in range(m // 2):
				ans[n - 1][2 * i] = al2[now]
				ans[n - 1][2 * i + 1] = al2[now]
				now ^= 1
			yoko -= m // 2
			n -= 1
	if m % 2 == 1:
		if tate < n // 2:
			print('NO')
			continue
		else:
			now = 0
			for i in range(n // 2):
				ans[2 * i][m - 1] = al2[now]
				ans[2 * i + 1][m - 1] = al2[now]
				now ^= 1
			tate -= n // 2
			m -= 1
	if tate % 2 == 1 or yoko % 2 == 1:
		print('NO')
		continue
	for i in range(n // 2):
		for j in range(m // 2):
			now = 0
			al = []
			for x in al3:
				if len(al) == 2:
					break
				flag = 1
				for di in range(2 * i - 2, 2 * i + 4):
					for dj in range(2 * j - 2, 2 * j + 4):
						if ans[di][dj] == x:
							flag = 0
				if flag:
					al.append(x)
			if tate > 0:
				ans[2 * i][2 * j] = al[now]
				ans[2 * i + 1][2 * j] = al[now]
				ans[2 * i][2 * j + 1] = al[now ^ 1]
				ans[2 * i + 1][2 * j + 1] = al[now ^ 1]
				tate -= 2
			else:
				ans[2 * i][2 * j] = al[now]
				ans[2 * i][2 * j + 1] = al[now]
				ans[2 * i + 1][2 * j] = al[now ^ 1]
				ans[2 * i + 1][2 * j + 1] = al[now ^ 1]
				yoko -= 2
	print('YES')
	for i in range(N):
		print(''.join(ans[i][:M]))


def ch(i):
	return chr(i + ord('a'))

def build(n, m, k):
	res = [['.' for i in range(m)] for j in range(n)]
	guide = [[27 for i in range(m // 2)] for j in range(n // 2)]
	cc = 0
	for (i, row) in enumerate(guide):
		for (j, cell) in enumerate(row):
			while i > 0 and guide[i - 1][j] == cc or (j > 0 and guide[i][j - 1] == cc):
				cc = (cc + 1) % 13
			guide[i][j] = cc
	for (i, row) in enumerate(guide):
		for (j, cell) in enumerate(row):
			if k > 0:
				res[2 * i][2 * j] = ch(2 * cell)
				res[2 * i][2 * j + 1] = ch(2 * cell)
				res[2 * i + 1][2 * j] = ch(2 * cell + 1)
				res[2 * i + 1][2 * j + 1] = ch(2 * cell + 1)
				k -= 2
			else:
				res[2 * i][2 * j] = ch(2 * cell)
				res[2 * i][2 * j + 1] = ch(2 * cell + 1)
				res[2 * i + 1][2 * j] = ch(2 * cell)
				res[2 * i + 1][2 * j + 1] = ch(2 * cell + 1)
	cc = 0
	if n % 2:
		for i in range(m // 2):
			while len(res) > 1 and (ch(cc) == res[-2][2 * i] or ch(cc) == res[-2][2 * i + 1]):
				cc = (cc + 1) % 26
			res[-1][2 * i] = ch(cc)
			res[-1][2 * i + 1] = ch(cc)
			cc = (cc + 1) % 26
	if m % 2:
		for i in range(n // 2):
			while len(res[0]) > 1 and (ch(cc) == res[2 * i][-2] or ch(cc) == res[2 * i + 1][-2]):
				cc = (cc + 1) % 26
			res[2 * i][-1] = ch(cc)
			res[2 * i + 1][-1] = ch(cc)
			cc = (cc + 1) % 26
	for i in res:
		print(''.join(i))

def solve(n, m, k):
	res = [[-1 for i in range(m)] for j in range(n)]
	ans = ''
	if n % 2:
		k -= m // 2
		if k >= 0 and k % 2 == 0 and (k <= (n - 1) * m // 2):
			print('YES')
			build(n, m, k)
		else:
			print('NO')
	elif m % 2:
		if k % 2 == 0 and k <= n * (m - 1) // 2:
			print('YES')
			build(n, m, k)
		else:
			print('NO')
	elif k % 2 == 0 and k <= n * m // 2:
		print('YES')
		build(n, m, k)
	else:
		print('NO')
t = int(input())
for i in range(t):
	(n, m, k) = [int(i) for i in input().split()]
	solve(n, m, k)


from string import ascii_lowercase

def main():
	(n_org, m_org, k) = map(int, input().split())
	n = n_org
	m = m_org
	ans = [[''] * m for _ in range(n)]
	cnt = 0
	if n_org % 2:
		if k < m_org // 2:
			print('NO')
			return
		else:
			for i in range(m_org // 2):
				ans[n_org - 1][i * 2] = ascii_lowercase[cnt]
				ans[n_org - 1][i * 2 + 1] = ascii_lowercase[cnt]
				cnt += 1
				cnt %= 26
			k -= m_org // 2
			n -= 1
	if m_org % 2:
		if n_org * m_org // 2 - k < n_org // 2:
			print('NO')
			return
		else:
			for i in range(n_org // 2):
				ans[i * 2][m_org - 1] = ascii_lowercase[cnt]
				ans[i * 2 + 1][m_org - 1] = ascii_lowercase[cnt]
				cnt += 1
				cnt %= 26
			m -= 1

	def ok(i, j, cnt):
		if i > 0:
			if ans[i - 1][j] == ascii_lowercase[cnt]:
				return False
			if ans[i - 1][j + 1] == ascii_lowercase[cnt]:
				return False
		if i < n_org - 2:
			if ans[i + 2][j] == ascii_lowercase[cnt]:
				return False
			if ans[i + 2][j + 1] == ascii_lowercase[cnt]:
				return False
		if j > 0:
			if ans[i][j - 1] == ascii_lowercase[cnt]:
				return False
			if ans[i + 1][j - 1] == ascii_lowercase[cnt]:
				return False
		if j < m_org - 2:
			if ans[i][j + 2] == ascii_lowercase[cnt]:
				return False
			if ans[i + 1][j + 2] == ascii_lowercase[cnt]:
				return False
		return True
	if n % 2 == 0 and m % 2 == 0:
		if k % 2 == 0:
			print('YES')
			(i2, j2) = (0, 0)
			if n != 0 and m != 0:
				for x in range(k // 2):
					while not ok(i2, j2, cnt):
						cnt += 1
						cnt %= 26
					ans[i2][j2] = ascii_lowercase[cnt]
					ans[i2][j2 + 1] = ascii_lowercase[cnt]
					cnt += 1
					cnt %= 26
					while not ok(i2, j2, cnt):
						cnt += 1
						cnt %= 26
					ans[i2 + 1][j2] = ascii_lowercase[cnt]
					ans[i2 + 1][j2 + 1] = ascii_lowercase[cnt]
					cnt += 1
					cnt %= 26
					j2 += 2
					if j2 > m - 1:
						j2 = 0
						i2 += 2
				while i2 < n:
					while not ok(i2, j2, cnt):
						cnt += 1
						cnt %= 26
					ans[i2][j2] = ascii_lowercase[cnt]
					ans[i2 + 1][j2] = ascii_lowercase[cnt]
					cnt += 1
					cnt %= 26
					while not ok(i2, j2, cnt):
						cnt += 1
						cnt %= 26
					ans[i2][j2 + 1] = ascii_lowercase[cnt]
					ans[i2 + 1][j2 + 1] = ascii_lowercase[cnt]
					cnt += 1
					cnt %= 26
					j2 += 2
					if j2 > m - 1:
						j2 = 0
						i2 += 2
			for ans_line in ans:
				print(''.join(ans_line))
		else:
			print('NO')
	return
t = int(input())
for i in range(t):
	main()


import sys
input = sys.stdin.readline

def domino(x, y, z, w):
	S = set()
	for (k, l) in [(x + 1, y), (x - 1, y), (x, y + 1), (x, y - 1), (z + 1, w), (z - 1, w), (z, w + 1), (z, w - 1)]:
		if 0 <= k < n and 0 <= l < m:
			S.add(ANS[k][l])
	for cc in 'abcdefghijklmnopqrstuvwxyz':
		if cc in S:
			continue
		else:
			break
	ANS[x][y] = cc
	ANS[z][w] = cc
t = int(input())
for tests in range(t):
	(n, m, k) = map(int, input().split())
	MAX = n * m // 2
	ANS = [[-1] * m for i in range(n)]
	if n % 2 == 1:
		for i in range(0, m, 2):
			domino(0, i, 0, i + 1)
			k -= 1
	elif m % 2 == 1:
		for i in range(0, n, 2):
			domino(i, 0, i + 1, 0)
	if k < 0 or k % 2 == 1:
		print('NO')
		continue
	for i in range(n):
		for j in range(m):
			if k > 0 and ANS[i][j] == -1:
				domino(i, j, i, j + 1)
				domino(i + 1, j, i + 1, j + 1)
				k -= 2
			elif ANS[i][j] == -1:
				domino(i, j, i + 1, j)
				domino(i, j + 1, i + 1, j + 1)
	if k != 0:
		print('NO')
	else:
		print('YES')
		for ans in ANS:
			print(''.join(ans))


from collections import deque
import heapq
from math import sqrt
import operator
from operator import itemgetter
import sys
import copy
inf_var = 0
if inf_var == 1:
	inf = open('input.txt', 'r')
else:
	inf = sys.stdin
input = inf.readline

def read_one_int():
	return int(input().rstrip('\n'))

def read_one_float():
	return float(input().rstrip('\n'))

def read_list_of_ints():
	res = [int(val) for val in input().rstrip('\n').split(' ')]
	return res

def read_str():
	return input().rstrip()

def in_field(field, i, j):
	return i >= 0 and j >= 0 and (i < len(field)) and (j < len(field[0]))

def get_next_ch(field, i1, j1, i2, j2):
	not_used = set('abcdefghijk')
	dx = [1, -1, 0, 0]
	dy = [0, 0, -1, 1]
	for i in range(len(dx)):
		cur_i = i1 + dx[i]
		cur_j = j1 + dy[i]
		if in_field(field, cur_i, cur_j):
			if field[cur_i][cur_j] is not None:
				if field[cur_i][cur_j] in not_used:
					not_used.remove(field[cur_i][cur_j])
		cur_i = i2 + dx[i]
		cur_j = j2 + dy[i]
		if in_field(field, cur_i, cur_j):
			if field[cur_i][cur_j] is not None:
				if field[cur_i][cur_j] in not_used:
					not_used.remove(field[cur_i][cur_j])
	return not_used.pop()

def main():
	tests = read_one_int()
	for _ in range(tests):
		(n, m, hor) = read_list_of_ints()
		field = [[None for _ in range(m)] for _ in range(n)]
		vert = n * m // 2 - hor
		square = n * m
		skip = None
		if n % 2:
			hor -= m // 2
			square -= m
			n -= 1
			if hor < 0:
				print('NO')
				continue
			for i in range(0, m, 2):
				cur_ch = get_next_ch(field, 0, i, 0, i + 1)
				field[0][i] = cur_ch
				field[0][i + 1] = cur_ch
				skip = 'hor'
		if m % 2:
			vert -= n // 2
			square -= n
			m -= 1
			if vert < 0:
				print('NO')
				continue
			for j in range(0, n, 2):
				cur_ch = get_next_ch(field, j, 0, j + 1, 0)
				field[j][0] = cur_ch
				field[j + 1][0] = cur_ch
				skip = 'vert'
		if not vert % 2 and (not hor % 2) and (square == (vert + hor) * 2):
			print('YES')
			st_i = 0
			st_j = 0
			if skip == 'hor':
				st_i = 1
			if skip == 'vert':
				st_j = 1
			for i in range(st_i, n, 2):
				for j in range(st_j, m, 2):
					if vert:
						cur_ch = get_next_ch(field, i, j, i + 1, j)
						field[i][j] = cur_ch
						field[i + 1][j] = cur_ch
						cur_ch = get_next_ch(field, i, j + 1, i + 1, j + 1)
						field[i][j + 1] = cur_ch
						field[i + 1][j + 1] = cur_ch
						vert -= 2
					else:
						cur_ch = get_next_ch(field, i, j, i, j + 1)
						field[i][j] = cur_ch
						field[i][j + 1] = cur_ch
						cur_ch = get_next_ch(field, i + 1, j, i + 1, j + 1)
						field[i + 1][j] = cur_ch
						field[i + 1][j + 1] = cur_ch
						hor -= 2
			for row in field:
				print(''.join(row))
		else:
			print('NO')
main()


import sys
import os
import math
from io import BytesIO, IOBase
from collections import defaultdict, Counter, deque
import bisect
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
t = int(input())
for i in range(t):
	(n, m, k) = map(int, input().split())
	n1 = n
	ans = [[''] * m for j in range(n)]
	flag = 0
	if n & 1:
		if m & 1 or 2 * k < m:
			print('NO')
			continue
		else:
			k -= m // 2
			for j in range(m):
				if j // 2 % 2 == 0:
					ans[n - 1][j] = 'y'
				else:
					ans[n - 1][j] = 'z'
			n -= 1
	if m & 1:
		for j in range(n):
			if j // 2 % 2 == 0:
				ans[j][m - 1] = 'y'
			else:
				ans[j][m - 1] = 'z'
		m -= 1
	for j in range(0, m, 2):
		if k >= n:
			k -= n
			if j // 2 % 2 == 0:
				for kk in range(n):
					if kk % 2 == 0:
						ans[kk][j] = ans[kk][j + 1] = 'a'
					else:
						ans[kk][j] = ans[kk][j + 1] = 'b'
			else:
				for kk in range(n):
					if kk % 2 == 0:
						ans[kk][j] = ans[kk][j + 1] = 'b'
					else:
						ans[kk][j] = ans[kk][j + 1] = 'a'
		else:
			if k % 2 == 0:
				flag = 1
				if j // 2 % 2 == 0:
					for kk in range(k):
						if kk % 2 == 0:
							ans[kk][j] = ans[kk][j + 1] = 'a'
						else:
							ans[kk][j] = ans[kk][j + 1] = 'b'
				else:
					for kk in range(k):
						if kk % 2 == 0:
							ans[kk][j] = ans[kk][j + 1] = 'b'
						else:
							ans[kk][j] = ans[kk][j + 1] = 'a'
				for kk in range(k, n):
					if kk // 2 % 2 == 0:
						ans[kk][j] = 'c'
						ans[kk][j + 1] = 'd'
					else:
						ans[kk][j] = 'd'
						ans[kk][j + 1] = 'c'
				for jj in range(j + 2, m, 2):
					for kk in range(n):
						if kk // 2 % 2 == 0:
							ans[kk][jj] = 'e'
							ans[kk][jj + 1] = 'f'
						else:
							ans[kk][jj] = 'f'
							ans[kk][jj + 1] = 'e'
			break
	else:
		if k == 0:
			flag = 1
	if flag == 0:
		print('NO')
	else:
		print('YES')
		for j in range(n1):
			print(''.join(ans[j]))


import sys, os
from math import *
from bisect import *
from heapq import *
from collections import *
if os.path.exists('in.txt'):
	sys.stdin = open('in.txt', 'r')
from io import BytesIO, IOBase

def main():
	for _ in range(int(input())):
		(n, m, k) = MI()
		p = m // 2
		ans = False
		if k == 0:
			if n % 2 == 0:
				ans = True
		elif m % 2:
			if k % 2 == 0 and p * n >= k:
				ans = True
		elif n % 2:
			k -= p
			if k >= 0 and k % 2 == 0:
				ans = True
		elif k % 2 == 0:
			ans = True
		if ans:
			print('YES')
			out = [['.' for j in range(m)] for i in range(n)]

			def rec(y):
				(i, j) = (0, 0)
				while y:
					nn = set()
					if i - 1 >= 0:
						nn.add(out[i - 1][j])
					if j - 1 >= 0:
						nn.add(out[i][j - 1])
					ch = 97
					while chr(ch) in nn:
						ch += 1
					ch = chr(ch)
					nn = set([ch])
					if j - 1 >= 0:
						nn.add(out[i + 1][j - 1])
					out[i][j] = ch
					out[i][j + 1] = ch
					ch = 97
					while chr(ch) in nn:
						ch += 1
					ch = chr(ch)
					out[i + 1][j] = ch
					out[i + 1][j + 1] = ch
					y -= 2
					j += 2
					if j + 1 >= m:
						j = 0
						i += 2
			rec(k)
			for i in range(n):
				for j in range(m):
					if out[i][j] != '.':
						continue
					nn = set()
					if i - 1 >= 0:
						nn.add(out[i - 1][j])
					if i + 1 >= n:
						continue
					if j - 1 >= 0:
						nn.add(out[i][j - 1])
						nn.add(out[i + 1][j - 1])
					ch = 97
					while chr(ch) in nn:
						ch += 1
					ch = chr(ch)
					out[i][j] = ch
					out[i + 1][j] = ch
			if out[-1][0] == '.':
				i = n - 1
				j = 0
				while j < m:
					nn = set()
					if i - 1 >= 0:
						nn.add(out[i - 1][j])
						nn.add(out[i - 1][j + 1])
					if j - 1 >= 0:
						nn.add(out[i][j - 1])
					ch = 97
					while chr(ch) in nn:
						ch += 1
					ch = chr(ch)
					out[i][j] = ch
					out[i][j + 1] = ch
					j += 2
			for i in out:
				print(''.join(i))
		else:
			print('NO')
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')

def MI():
	return map(int, input().split())

def outP(var):
	sys.stdout.write(str(var) + '\n')
MOD = 10 ** 9 + 7
mod = 998244353
main()


import os
import sys
from io import BytesIO, IOBase
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
t = int(input())
while t:
	t -= 1
	(n, m, k) = [int(x) for x in input().split()]
	if n % 2 == m % 2 == 0:
		ans = [[0 for x in range(m)] for x in range(n)]
		arr = [[0 for x in range(m)] for x in range(n)]
		for i in range(0, n, 2):
			for j in range(0, m, 2):
				if i == j == 0:
					arr[i][j] = 0
				elif i == 0:
					arr[i][j] = (arr[i][j - 2] + 1) % 2
				else:
					arr[i][j] = (arr[i - 2][j] + 1) % 2
		if k % 2 == 0:
			print('YES')
			for i in range(0, n, 2):
				if not k:
					break
				for j in range(0, m, 2):
					if not k:
						break
					if arr[i][j] == 0:
						curr = 'ab'
					else:
						curr = 'cd'
					ans[i][j] = curr[0]
					ans[i][j + 1] = curr[0]
					ans[i + 1][j] = curr[1]
					ans[i + 1][j + 1] = curr[1]
					k -= 2
			for i in range(0, n, 2):
				for j in range(0, m, 2):
					if ans[i][j] != 0:
						continue
					if arr[i][j] == 0:
						curr = 'mn'
					else:
						curr = 'xy'
					ans[i][j] = curr[0]
					ans[i][j + 1] = curr[1]
					ans[i + 1][j] = curr[0]
					ans[i + 1][j + 1] = curr[1]
			for i in range(n):
				for j in range(m):
					sys.stdout.write(ans[i][j])
				sys.stdout.write('\n')
		else:
			print('NO')
	else:
		s = False
		if n % 2 == 0:
			(n, m) = (m, n)
			k = n * m / 2 - k
			s = True
		k -= m // 2
		ans = [[0 for x in range(m)] for x in range(n)]
		arr = [[0 for x in range(m)] for x in range(n)]
		for i in range(0, n, 2):
			for j in range(0, m, 2):
				if i == j == 0:
					arr[i][j] = 0
				elif i == 0:
					arr[i][j] = (arr[i][j - 2] + 1) % 2
				else:
					arr[i][j] = (arr[i - 2][j] + 1) % 2
		if k < 0:
			print('NO')
			continue
		for j in range(0, m, 2):
			if arr[0][j] == 0:
				curr = 'kk'
			else:
				curr = 'zz'
			ans[0][j] = curr[0]
			ans[0][j + 1] = curr[1]
		if k % 2 == 0:
			print('YES')
			for i in range(1, n, 2):
				if not k:
					break
				for j in range(0, m, 2):
					if not k:
						break
					if arr[i - 1][j] == 0:
						curr = 'ab'
					else:
						curr = 'cd'
					ans[i][j] = curr[0]
					ans[i][j + 1] = curr[0]
					ans[i + 1][j] = curr[1]
					ans[i + 1][j + 1] = curr[1]
					k -= 2
			for i in range(1, n, 2):
				for j in range(0, m, 2):
					if ans[i][j] != 0:
						continue
					if arr[i - 1][j] == 0:
						curr = 'mn'
					else:
						curr = 'xy'
					ans[i][j] = curr[0]
					ans[i][j + 1] = curr[1]
					ans[i + 1][j] = curr[0]
					ans[i + 1][j + 1] = curr[1]
			if s:
				for j in range(m):
					for i in range(n):
						sys.stdout.write(ans[i][j])
					sys.stdout.write('\n')
			else:
				for i in range(n):
					for j in range(m):
						sys.stdout.write(ans[i][j])
					sys.stdout.write('\n')
		else:
			print('NO')


import sys
import math
mod = 10 ** 9 + 7
LI = lambda : [int(k) for k in input().split()]
input = lambda : sys.stdin.readline().rstrip()
IN = lambda : int(input())
S = lambda : input()
r = range
alp = 'abcdefghijklmnopqrstuvwxyz'

def pfn(plc):
	for i in range(len(plc)):
		for j in range(len(plc[i])):
			if plc[i][j] == 'hor':
				plc[i][j] = alp[(i + j) % 26]
				plc[i][j + 1] = alp[(i + j) % 26]
			elif plc[i][j] == 'ver':
				plc[i][j] = alp[(i + j) % 26]
				plc[i + 1][j] = alp[(i + j) % 26]
			print(plc[i][j], end='')
		print('')
for t in r(IN()):
	(n, m, k) = LI()
	plc = [['ver'] * m for i in range(n)]
	if n % 2 == 0 and m % 2 == 0:
		if k % 2 == 0:
			print('YES')
			ind = 0
			i = 0
			j = 0
			while k:
				plc[i][j] = 'hor'
				plc[i][j + 1] = 'hor'
				k -= 1
				ind += 1
				j = ind // n * 2
				i = ind % n
			pfn(plc)
		else:
			print('NO')
	elif n % 2 == 1:
		if k >= m // 2:
			k -= m // 2
			if k % 2 == 0:
				print('YES')
				j = 0
				tl = m // 2
				while tl:
					plc[-1][j] = 'hor'
					plc[-1][j + 1] = 'hor'
					j += 2
					tl -= 1
				n -= 1
				ind = 0
				i = 0
				j = 0
				while k:
					plc[i][j] = 'hor'
					plc[i][j + 1] = 'hor'
					k -= 1
					ind += 1
					j = ind // n * 2
					i = ind % n
				pfn(plc)
			else:
				print('NO')
		else:
			print('NO')
	elif k <= (m - 1) * n // 2:
		if k % 2 == 0:
			print('YES')
			ind = 0
			i = 0
			j = 0
			while k:
				plc[i][j] = 'hor'
				plc[i][j + 1] = 'hor'
				k -= 1
				ind += 1
				j = ind // n * 2
				i = ind % n
			pfn(plc)
		else:
			print('NO')
	else:
		print('NO')


t = int(input())
let = ['a', 'b']
lett = ['c', 'd']
for i in range(t):
	(n, m, k) = [int(j) for j in input().split()]
	if n % 2 == 1:
		if m / 2 <= k and m / 2 % 2 == k % 2:
			print('YES')
			c = 0
			kp = [1 for j in range(m // 2)]
			k -= m // 2
			while k != 0:
				if kp[c] < n:
					k -= 1
					kp[c] += 1
				else:
					c += 1
			res = [[0 for j in range(m)] for ii in range(n)]
			for x in range(m):
				for y in range(n):
					res[y][x] = lett[abs((y + 1) // 2 % 2 - x % 2)]
			for j in range(m // 2):
				for ii in range(kp[j]):
					res[ii][j * 2] = let[abs(ii % 2 - j % 2)]
					res[ii][j * 2 + 1] = let[abs(ii % 2 - j % 2)]
			for j in res:
				print(''.join((str(ii) for ii in j)))
		else:
			print('NO')
	elif m % 2 == 0:
		if k % 2 == 0:
			print('YES')
			c = 0
			kp = [0 for j in range(m // 2)]
			while k != 0:
				if kp[c] < n:
					k -= 1
					kp[c] += 1
				else:
					c += 1
			res = [[0 for j in range(m)] for ii in range(n)]
			for x in range(m):
				for y in range(n):
					res[y][x] = lett[abs(y // 2 % 2 - x % 2)]
			for j in range(m // 2):
				for ii in range(kp[j]):
					res[ii][j * 2] = let[abs(ii % 2 - j % 2)]
					res[ii][j * 2 + 1] = let[abs(ii % 2 - j % 2)]
			for j in res:
				print(''.join((str(ii) for ii in j)))
		else:
			print('NO')
	elif n / 2 <= n * m / 2 - k and n / 2 % 2 == (n * m / 2 - k) % 2:
		print('YES')
		(n, m, k) = (m, n, n * m / 2 - k)
		c = 0
		kp = [1 for j in range(m // 2)]
		k -= m // 2
		while k != 0:
			if kp[c] < n:
				k -= 1
				kp[c] += 1
			else:
				c += 1
		res = [[0 for j in range(m)] for ii in range(n)]
		for x in range(m):
			for y in range(n):
				res[y][x] = lett[abs((y + 1) // 2 % 2 - x % 2)]
		for j in range(m // 2):
			for ii in range(kp[j]):
				res[ii][j * 2] = let[abs(ii % 2 - j % 2)]
				res[ii][j * 2 + 1] = let[abs(ii % 2 - j % 2)]
		ress = [[0 for x in range(n)] for y in range(m)]
		for y in range(n):
			for x in range(m):
				ress[x][y] = res[y][x]
		for j in ress:
			print(''.join((str(ii) for ii in j)))
	else:
		print('NO')


from os import path
from io import BytesIO, IOBase
import sys
from heapq import heappush, heappop
from functools import cmp_to_key as ctk
from collections import deque, Counter, defaultdict as dd
from bisect import bisect, bisect_left, bisect_right, insort, insort_left, insort_right
from itertools import permutations
from datetime import datetime
from math import ceil, sqrt, log, gcd

def ii():
	return int(input())

def si():
	return input().rstrip()

def mi():
	return map(int, input().split())

def li():
	return list(mi())
abc = 'abcdefghijklmnopqrstuvwxyz'
mod = 1000000007
inf = float('inf')
vow = ['a', 'e', 'i', 'o', 'u']
(dx, dy) = ([-1, 1, 0, 0], [0, 0, 1, -1])

def bo(i):
	return ord(i) - ord('0')
file = 1

def ceil(a, b):
	return (a + b - 1) // b

def solve():
	for _ in range(1, ii() + 1):
		(n, m, k) = mi()
		if n == 1:
			if k == m // 2:
				print('YES')
				for i in range(m // 2):
					if i % 2 == 0:
						print('aa', end='')
					else:
						print('bb', end='')
				print()
			else:
				print('NO')
			continue
		if m == 1:
			if k == 0:
				print('YES')
				for i in range(n // 2):
					if i % 2 == 0:
						print('a')
						print('a')
					else:
						print('b')
						print('b')
			else:
				print('NO')
			continue
		n1 = n
		k1 = k
		if n & 1:
			k -= m // 2
			n -= 1
		if k < 0:
			print('NO')
			continue
		col = n
		ok = True
		for i in range(m // 2):
			if k < col:
				rem = col - k
				k = 0
				if rem & 1:
					ok = False
				break
			k -= col
		if ok and k == 0:
			print('YES')
			x = [['0'] * m for i in range(n1)]
			if n1 & 1:
				c = 0
				for i in range(m // 2):
					if i % 2 == 0:
						x[0][c] = x[0][c + 1] = 'a'
					else:
						x[0][c] = x[0][c + 1] = 'b'
					c += 2
				k1 -= m // 2
			if m & 1:
				c = 0
				for j in range(n1 // 2):
					if j % 2 == 0:
						x[c][-1] = x[c + 1][-1] = 'i'
					else:
						x[c][-1] = x[c + 1][-1] = 'j'
					c += 2
			for i in range(n1 % 2, n1, 2):
				c = 0
				for j in range(m // 2):
					if k1 == 0:
						break
					if j % 2 == 0:
						x[i][c] = x[i][c + 1] = 'p'
						x[i + 1][c] = x[i + 1][c + 1] = 'q'
					else:
						x[i][c] = x[i][c + 1] = 'q'
						x[i + 1][c] = x[i + 1][c + 1] = 'p'
					k1 -= 2
					c += 2
				if k1 == 0:
					for j in range(m):
						if x[i][j] != '0':
							continue
						if j % 2 == 0:
							x[i][j] = x[i + 1][j] = 'c'
						else:
							x[i][j] = x[i + 1][j] = 'd'
				if k1 == 0:
					break
			i = 0
			(c1, c2) = ('g', 'h')
			while i < n1:
				if x[i][0] != '0':
					i += 1
					continue
				for j in range(m):
					if j % 2 == 0:
						x[i][j] = x[i + 1][j] = c1
					else:
						x[i][j] = x[i + 1][j] = c2
				(c1, c2) = (c2, c1)
				i += 2
			for i in range(n1):
				print(''.join(x[i]))
		else:
			print('NO')
if file:
	if path.exists('input.txt'):
		sys.stdin = open('input.txt', 'r')
		sys.stdout = open('output.txt', 'w')
	else:
		input = sys.stdin.readline
solve()


import sys
import math
from math import factorial, inf, gcd, sqrt
from heapq import *
from functools import *
from itertools import *
from collections import *
from typing import *
from bisect import *
import random
from sys import stdin, stdout
sys.setrecursionlimit(10 ** 5)

def inp():
	return stdin.readline().strip()

def iinp():
	return int(inp())

def mp():
	return map(int, inp().split())

def lmp():
	return list(mp())

def f(ans, x, y, n, m, k):
	s = 'b'
	for j in range(y, m, 2):
		s = 'b' if s == 'a' else 'a'
		t = s
		for i in range(x, n):
			if k == 0:
				break
			ans[i][j] = ans[i][j + 1] = t
			t = 'b' if t == 'a' else 'a'
			k -= 1
		if k == 0:
			break
	s = 'g'
	for i in range(x, n, 2):
		s = 'g' if s == 'h' else 'h'
		t = s
		for j in range(y, m):
			if ans[i][j] == 'z':
				ans[i][j] = ans[i + 1][j] = t
			t = 'g' if t == 'h' else 'h'
ti = int(input())
for i in range(ti):
	(n, m, k) = mp()
	ans = [['z'] * m for i in range(n)]
	if n % 2 == 1:
		t = m // 2
		if k >= t and (k - t) % 2 == 0:
			print('YES')
			s = 'x'
			for j in range(0, m, 2):
				ans[0][j] = ans[0][j + 1] = s
				s = 'y' if s == 'x' else 'x'
			f(ans, 1, 0, n, m, k - t)
			for i in ans:
				print(''.join(i))
		else:
			print('NO')
	elif m % 2 == 1:
		if k % 2 == 0 and k + n // 2 <= m * n // 2:
			print('YES')
			s = 'x'
			for j in range(0, n, 2):
				ans[j][0] = ans[j + 1][0] = s
				s = 'y' if s == 'x' else 'x'
			f(ans, 0, 1, n, m, k)
			for i in ans:
				print(''.join(i))
		else:
			print('NO')
	elif k % 2 == 0:
		print('YES')
		f(ans, 0, 0, n, m, k)
		for i in ans:
			print(''.join(i))
	else:
		print('NO')


import math
import random
import heapq, bisect
import sys
from collections import deque, defaultdict
from fractions import Fraction
import sys
import threading
from collections import defaultdict
threading.stack_size(10 ** 8)
mod = 10 ** 9 + 7
mod1 = 998244353
import os
import sys
from io import BytesIO, IOBase
sys.setrecursionlimit(300000)
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')

class TreeNode:

	def __init__(self, k, v):
		self.key = k
		self.value = v
		self.left = None
		self.right = None
		self.parent = None
		self.height = 1
		self.num_left = 1
		self.num_total = 1

class AvlTree:

	def __init__(self):
		self._tree = None

	def add(self, k, v):
		if not self._tree:
			self._tree = TreeNode(k, v)
			return
		node = self._add(k, v)
		if node:
			self._rebalance(node)

	def _add(self, k, v):
		node = self._tree
		while node:
			if k < node.key:
				if node.left:
					node = node.left
				else:
					node.left = TreeNode(k, v)
					node.left.parent = node
					return node.left
			elif node.key < k:
				if node.right:
					node = node.right
				else:
					node.right = TreeNode(k, v)
					node.right.parent = node
					return node.right
			else:
				node.value = v
				return

	@staticmethod
	def get_height(x):
		return x.height if x else 0

	@staticmethod
	def get_num_total(x):
		return x.num_total if x else 0

	def _rebalance(self, node):
		n = node
		while n:
			lh = self.get_height(n.left)
			rh = self.get_height(n.right)
			n.height = max(lh, rh) + 1
			balance_factor = lh - rh
			n.num_total = 1 + self.get_num_total(n.left) + self.get_num_total(n.right)
			n.num_left = 1 + self.get_num_total(n.left)
			if balance_factor > 1:
				if self.get_height(n.left.left) < self.get_height(n.left.right):
					self._rotate_left(n.left)
				self._rotate_right(n)
			elif balance_factor < -1:
				if self.get_height(n.right.right) < self.get_height(n.right.left):
					self._rotate_right(n.right)
				self._rotate_left(n)
			else:
				n = n.parent

	def _remove_one(self, node):
		replacement = node.left or node.right
		if node.parent:
			if AvlTree._is_left(node):
				node.parent.left = replacement
			else:
				node.parent.right = replacement
			replacement.parent = node.parent
			node.parent = None
		else:
			self._tree = replacement
			replacement.parent = None
		node.left = None
		node.right = None
		node.parent = None
		self._rebalance(replacement)

	def _remove_leaf(self, node):
		if node.parent:
			if AvlTree._is_left(node):
				node.parent.left = None
			else:
				node.parent.right = None
			self._rebalance(node.parent)
		else:
			self._tree = None
		node.parent = None
		node.left = None
		node.right = None

	def remove(self, k):
		node = self._get_node(k)
		if not node:
			return
		if AvlTree._is_leaf(node):
			self._remove_leaf(node)
			return
		if node.left and node.right:
			nxt = AvlTree._get_next(node)
			node.key = nxt.key
			node.value = nxt.value
			if self._is_leaf(nxt):
				self._remove_leaf(nxt)
			else:
				self._remove_one(nxt)
			self._rebalance(node)
		else:
			self._remove_one(node)

	def get(self, k):
		node = self._get_node(k)
		return node.value if node else -1

	def _get_node(self, k):
		if not self._tree:
			return None
		node = self._tree
		while node:
			if k < node.key:
				node = node.left
			elif node.key < k:
				node = node.right
			else:
				return node
		return None

	def get_at(self, pos):
		x = pos + 1
		node = self._tree
		while node:
			if x < node.num_left:
				node = node.left
			elif node.num_left < x:
				x -= node.num_left
				node = node.right
			else:
				return (node.key, node.value)
		raise IndexError('Out of ranges')

	@staticmethod
	def _is_left(node):
		return node.parent.left and node.parent.left == node

	@staticmethod
	def _is_leaf(node):
		return node.left is None and node.right is None

	def _rotate_right(self, node):
		if not node.parent:
			self._tree = node.left
			node.left.parent = None
		elif AvlTree._is_left(node):
			node.parent.left = node.left
			node.left.parent = node.parent
		else:
			node.parent.right = node.left
			node.left.parent = node.parent
		bk = node.left.right
		node.left.right = node
		node.parent = node.left
		node.left = bk
		if bk:
			bk.parent = node
		node.height = max(self.get_height(node.left), self.get_height(node.right)) + 1
		node.num_total = 1 + self.get_num_total(node.left) + self.get_num_total(node.right)
		node.num_left = 1 + self.get_num_total(node.left)

	def _rotate_left(self, node):
		if not node.parent:
			self._tree = node.right
			node.right.parent = None
		elif AvlTree._is_left(node):
			node.parent.left = node.right
			node.right.parent = node.parent
		else:
			node.parent.right = node.right
			node.right.parent = node.parent
		bk = node.right.left
		node.right.left = node
		node.parent = node.right
		node.right = bk
		if bk:
			bk.parent = node
		node.height = max(self.get_height(node.left), self.get_height(node.right)) + 1
		node.num_total = 1 + self.get_num_total(node.left) + self.get_num_total(node.right)
		node.num_left = 1 + self.get_num_total(node.left)

	@staticmethod
	def _get_next(node):
		if not node.right:
			return node.parent
		n = node.right
		while n.left:
			n = n.left
		return n

class SegmentTree1:

	def __init__(self, data, default=2 * 10 ** 9, func=lambda a, b: min(a, b)):
		self._default = default
		self._func = func
		self._len = len(data)
		self._size = _size = 1 << (self._len - 1).bit_length()
		self.data = [default] * (2 * _size)
		self.data[_size:_size + self._len] = data
		for i in reversed(range(_size)):
			self.data[i] = func(self.data[i + i], self.data[i + i + 1])

	def __delitem__(self, idx):
		self[idx] = self._default

	def __getitem__(self, idx):
		return self.data[idx + self._size]

	def __setitem__(self, idx, value):
		idx += self._size
		self.data[idx] = value
		idx >>= 1
		while idx:
			self.data[idx] = self._func(self.data[2 * idx], self.data[2 * idx + 1])
			idx >>= 1

	def __len__(self):
		return self._len

	def query(self, start, stop):
		if start == stop:
			return self.__getitem__(start)
		stop += 1
		start += self._size
		stop += self._size
		res = self._default
		while start < stop:
			if start & 1:
				res = self._func(res, self.data[start])
				start += 1
			if stop & 1:
				stop -= 1
				res = self._func(res, self.data[stop])
			start >>= 1
			stop >>= 1
		return res

	def __repr__(self):
		return 'SegmentTree({0})'.format(self.data)

class SegmentTree:

	def __init__(self, data, default=-1, func=lambda a, b: max(a, b)):
		self._default = default
		self._func = func
		self._len = len(data)
		self._size = _size = 1 << (self._len - 1).bit_length()
		self.data = [default] * (2 * _size)
		self.data[_size:_size + self._len] = data
		for i in reversed(range(_size)):
			self.data[i] = func(self.data[i + i], self.data[i + i + 1])

	def __delitem__(self, idx):
		self[idx] = self._default

	def __getitem__(self, idx):
		return self.data[idx + self._size]

	def __setitem__(self, idx, value):
		idx += self._size
		self.data[idx] = value
		idx >>= 1
		while idx:
			self.data[idx] = self._func(self.data[2 * idx], self.data[2 * idx + 1])
			idx >>= 1

	def __len__(self):
		return self._len

	def query(self, start, stop):
		if start == stop:
			return self.__getitem__(start)
		stop += 1
		start += self._size
		stop += self._size
		res = self._default
		while start < stop:
			if start & 1:
				res = self._func(res, self.data[start])
				start += 1
			if stop & 1:
				stop -= 1
				res = self._func(res, self.data[stop])
			start >>= 1
			stop >>= 1
		return res

	def __repr__(self):
		return 'SegmentTree({0})'.format(self.data)

class Factorial:

	def __init__(self, MOD):
		self.MOD = MOD
		self.factorials = [1, 1]
		self.invModulos = [0, 1]
		self.invFactorial_ = [1, 1]

	def calc(self, n):
		if n <= -1:
			print('Invalid argument to calculate n!')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		if n < len(self.factorials):
			return self.factorials[n]
		nextArr = [0] * (n + 1 - len(self.factorials))
		initialI = len(self.factorials)
		prev = self.factorials[-1]
		m = self.MOD
		for i in range(initialI, n + 1):
			prev = nextArr[i - initialI] = prev * i % m
		self.factorials += nextArr
		return self.factorials[n]

	def inv(self, n):
		if n <= -1:
			print('Invalid argument to calculate n^(-1)')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		p = self.MOD
		pi = n % p
		if pi < len(self.invModulos):
			return self.invModulos[pi]
		nextArr = [0] * (n + 1 - len(self.invModulos))
		initialI = len(self.invModulos)
		for i in range(initialI, min(p, n + 1)):
			next = -self.invModulos[p % i] * (p // i) % p
			self.invModulos.append(next)
		return self.invModulos[pi]

	def invFactorial(self, n):
		if n <= -1:
			print('Invalid argument to calculate (n^(-1))!')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		if n < len(self.invFactorial_):
			return self.invFactorial_[n]
		self.inv(n)
		nextArr = [0] * (n + 1 - len(self.invFactorial_))
		initialI = len(self.invFactorial_)
		prev = self.invFactorial_[-1]
		p = self.MOD
		for i in range(initialI, n + 1):
			prev = nextArr[i - initialI] = prev * self.invModulos[i % p] % p
		self.invFactorial_ += nextArr
		return self.invFactorial_[n]

class Combination:

	def __init__(self, MOD):
		self.MOD = MOD
		self.factorial = Factorial(MOD)

	def ncr(self, n, k):
		if k < 0 or n < k:
			return 0
		k = min(k, n - k)
		f = self.factorial
		return f.calc(n) * f.invFactorial(max(n - k, k)) * f.invFactorial(min(k, n - k)) % self.MOD

def powm(a, n, m):
	if a == 1 or n == 0:
		return 1
	if n % 2 == 0:
		s = powm(a, n // 2, m)
		return s * s % m
	else:
		return a * powm(a, n - 1, m) % m

def sort_list(list1, list2):
	zipped_pairs = zip(list2, list1)
	z = [x for (_, x) in sorted(zipped_pairs)]
	return z

def product(l):
	por = 1
	for i in range(len(l)):
		por *= l[i]
	return por

def binarySearchCount(arr, n, key):
	left = 0
	right = n - 1
	count = 0
	while left <= right:
		mid = int((right + left) / 2)
		if arr[mid] < key:
			count = mid + 1
			left = mid + 1
		else:
			right = mid - 1
	return count

def countdig(n):
	c = 0
	while n > 0:
		n //= 10
		c += 1
	return c

def binary(x, length):
	y = bin(x)[2:]
	return y if len(y) >= length else '0' * (length - len(y)) + y

def countGreater(arr, n, k):
	l = 0
	r = n - 1
	leftGreater = n
	while l <= r:
		m = int(l + (r - l) / 2)
		if arr[m] >= k:
			leftGreater = m
			r = m - 1
		else:
			l = m + 1
	return n - leftGreater

class TrieNode:

	def __init__(self):
		self.children = [None] * 26
		self.isEndOfWord = False

class Trie:

	def __init__(self):
		self.root = self.getNode()

	def getNode(self):
		return TrieNode()

	def _charToIndex(self, ch):
		return ord(ch) - ord('a')

	def insert(self, key):
		pCrawl = self.root
		length = len(key)
		for level in range(length):
			index = self._charToIndex(key[level])
			if not pCrawl.children[index]:
				pCrawl.children[index] = self.getNode()
			pCrawl = pCrawl.children[index]
		pCrawl.isEndOfWord = True

	def search(self, key):
		pCrawl = self.root
		length = len(key)
		for level in range(length):
			index = self._charToIndex(key[level])
			if not pCrawl.children[index]:
				return False
			pCrawl = pCrawl.children[index]
		return pCrawl != None and pCrawl.isEndOfWord

class Node:

	def __init__(self, data):
		self.data = data
		self.count = 0
		self.left = None
		self.right = None

class BinaryTrie:

	def __init__(self):
		self.root = Node(0)

	def insert(self, pre_xor):
		self.temp = self.root
		for i in range(31, -1, -1):
			val = pre_xor & 1 << i
			if val:
				if not self.temp.right:
					self.temp.right = Node(0)
				self.temp = self.temp.right
				self.temp.count += 1
			if not val:
				if not self.temp.left:
					self.temp.left = Node(0)
				self.temp = self.temp.left
				self.temp.count += 1
		self.temp.data = pre_xor

	def query(self, xor):
		self.temp = self.root
		for i in range(31, -1, -1):
			val = xor & 1 << i
			if not val:
				if self.temp.left and self.temp.left.count > 0:
					self.temp = self.temp.left
				elif self.temp.right:
					self.temp = self.temp.right
			elif self.temp.right and self.temp.right.count > 0:
				self.temp = self.temp.right
			elif self.temp.left:
				self.temp = self.temp.left
			self.temp.count -= 1
		return xor ^ self.temp.data
for ik in range(int(input())):
	(n, m, k) = map(int, input().split())

	def find(n, m, k):
		if n % 2 == 1:
			k -= m // 2
			if k < 0:
				return False
		poss = (m - m % 2) // 2
		if k % 2 == 0 and k <= n * poss:
			return True
		return False
	if find(n, m, k) == True:
		print('YES')
		ans = [['' for i in range(m)] for j in range(n)]
		ch = 0
		if n % 2 == 1:
			for i in range(0, m, 2):
				ans[0][i] = chr(ch + 97)
				ans[0][i + 1] = chr(ch + 97)
				ch += 1
				ch %= 26
			k -= m // 2
		ch = 0
		for i in range(n % 2, n, 2):
			for j in range(0, m, 2):
				while i > 0 and chr(ch + 97) == ans[i - 1][j]:
					ch += 1
					ch %= 26
				if k > 0 and j < m - 1:
					ans[i][j] = chr(ch + 97)
					ans[i][j + 1] = chr(ch + 97)
					ch = (ch + 1) % 26
					ans[i + 1][j] = chr(ch + 97)
					ans[i + 1][j + 1] = chr(ch + 97)
					k -= 2
					ch += 1
					ch %= 26
				else:
					break
		for i in range(n % 2, n, 2):
			for j in range(m):
				ch = 0
				if ans[i][j] == '':
					while i > 0 and chr(ch + 97) == ans[i - 1][j] or (j > 0 and chr(ch + 97) == ans[i][j - 1]) or (j > 0 and chr(ch + 97) == ans[i + 1][j - 1]):
						ch += 1
						ch %= 26
					ans[i][j] = chr(ch + 97)
					ans[i + 1][j] = chr(ch + 97)
					ch += 1
					ch %= 26
		for i in range(n):
			print(*ans[i], sep='')
	else:
		print('NO')


import os
import sys
from io import BytesIO, IOBase
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'a1' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline()

def RL():
	return map(int, sys.stdin.readline().split())

def RLL():
	return list(map(int, sys.stdin.readline().split()))

def N():
	return int(input())

def S():
	return input().strip()

def print_list(l):
	print(' '.join(map(str, l)))
from heapq import *
from collections import deque as dq
from math import ceil, floor, sqrt, pow, factorial, log2
import bisect as bs
from collections import Counter
from itertools import permutations
for _ in range(N()):
	(n, m, k) = RL()
	rows = n
	cols = m
	h = k
	v = n * m // 2 - k
	if n % 2 == 1:
		k -= m // 2
	if m % 2 == 1:
		v -= n // 2
	if v >= 0 and k >= 0 and (k % 2 == 0) and (v % 2 == 0):
		print('YES')
		v = n * m // 2 - h
		mat = [['' for i in range(m)] for j in range(n)]
		if n % 2 == 1:
			row = ['x', 'x', 'y', 'y']
			point = 0
			h -= m // 2
			for i in range(m):
				mat[-1][i] = row[point]
				point += 1
				point = point % 4
			n -= 1
		if m % 2 == 1:
			v -= n // 2
			col = ['x', 'x', 'y', 'y']
			point = 0
			for i in range(n):
				mat[i][-1] = col[point]
				point += 1
				point = point % 4
			m -= 1
		choice1 = ['a', 'b']
		choice2 = ['c', 'd']
		flag1 = 1
		for i in range(0, n, 2):
			flag2 = 1
			if flag1:
				for j in range(0, m, 2):
					if flag2:
						if h:
							mat[i][j] = 'a'
							mat[i][j + 1] = 'a'
							mat[i + 1][j] = 'b'
							mat[i + 1][j + 1] = 'b'
							h -= 2
						else:
							mat[i][j] = 'a'
							mat[i][j + 1] = 'b'
							mat[i + 1][j] = 'a'
							mat[i + 1][j + 1] = 'b'
							v -= 2
					elif h:
						mat[i][j] = 'c'
						mat[i][j + 1] = 'c'
						mat[i + 1][j] = 'd'
						mat[i + 1][j + 1] = 'd'
						h -= 2
					else:
						mat[i][j] = 'c'
						mat[i][j + 1] = 'd'
						mat[i + 1][j] = 'c'
						mat[i + 1][j + 1] = 'd'
						v -= 2
					flag2 = not flag2
			else:
				for j in range(0, m, 2):
					if flag2:
						if h:
							mat[i][j] = 'c'
							mat[i][j + 1] = 'c'
							mat[i + 1][j] = 'd'
							mat[i + 1][j + 1] = 'd'
							h -= 2
						else:
							mat[i][j] = 'c'
							mat[i][j + 1] = 'd'
							mat[i + 1][j] = 'c'
							mat[i + 1][j + 1] = 'd'
							v -= 2
					elif h:
						mat[i][j] = 'a'
						mat[i][j + 1] = 'a'
						mat[i + 1][j] = 'b'
						mat[i + 1][j + 1] = 'b'
						h -= 2
					else:
						mat[i][j] = 'a'
						mat[i][j + 1] = 'b'
						mat[i + 1][j] = 'a'
						mat[i + 1][j + 1] = 'b'
						v -= 2
					flag2 = not flag2
			flag1 = not flag1
		for i in range(rows):
			print(''.join(mat[i]))
	else:
		print('NO')


from itertools import product, permutations, combinations, accumulate, compress
import os, sys
input = lambda : sys.stdin.buffer.readline().rstrip(b'\r\n')

def dbp(*args, **kwargs):
	print(*args, file=sys.stderr, **kwargs)
a_str = lambda : input().decode('ascii')
get_int_list = lambda : [int(x) for x in input().split()]
join_str = lambda l, ch=' ': ch.join((str(x) for x in l))

def fill(h, w, horzs, verts):
	ans = ['YES']
	g = [['.'] * w for r in range(h)]
	cr = cc = 0
	if h % 2 == 1:
		l = 'z'
		for i in range(0, w, 2):
			g[0][i] = l
			g[0][i + 1] = l
			horzs -= 1
			l = 'y' if l == 'z' else 'z'
		cr = 1
	if w % 2 == 1:
		l = 'z'
		for i in range(0, h, 2):
			g[i][0] = l
			g[i + 1][0] = l
			verts -= 1
			l = 'y' if l == 'z' else 'z'
		cc = 1
	l = ord('a')
	for r in range(cr, h, 2):
		for c in range(cc, w, 2):
			borders = set()
			if r > 0:
				borders.add(g[r - 1][c])
				borders.add(g[r - 1][c + 1])
			if c > 0:
				borders.add(g[r][c - 1])
				borders.add(g[r + 1][c - 1])
			while chr(l) in borders:
				l = l + 1 if l < ord('j') else ord('a')
			l1 = chr(l)
			l = l + 1 if l < ord('j') else ord('a')
			while chr(l) in borders:
				l = l + 1 if l < ord('j') else ord('a')
			l2 = chr(l)
			if horzs:
				g[r][c] = l1
				g[r][c + 1] = l1
				g[r + 1][c] = l2
				g[r + 1][c + 1] = l2
				horzs -= 2
			else:
				g[r][c] = l1
				g[r + 1][c] = l1
				g[r][c + 1] = l2
				g[r + 1][c + 1] = l2
				verts -= 2
	assert horzs == verts == 0
	for r in g:
		ans.append(join_str(r, ''))
	return '\n'.join(ans)

def wa4(h, w, horzs, verts):
	if h % 2 == 1:
		horzs -= w // 2
		if horzs < 0 or horzs % 2 == 1 or verts % 2 == 1:
			return 'NO'
		else:
			return fill(h, w, horzs + w // 2, verts)
	elif w % 2 == 1:
		verts -= h // 2
		if verts < 0 or horzs % 2 == 1 or verts % 2 == 1:
			return 'NO'
		else:
			return fill(h, w, horzs, verts + h // 2)
	elif horzs % 2 == 0 == verts % 2:
		return fill(h, w, horzs, verts)
	else:
		return 'NO'

def do_thing():
	(h, w, k) = get_int_list()
	verts = h * w // 2 - k
	dbp('case:', h, w, k, verts)
	return wa4(h, w, k, verts)

def multicase():
	maxcc = int(input().strip())
	for cc in range(maxcc):
		print(do_thing())
multicase()


import os
import sys
import math
from io import BytesIO, IOBase
import io
from fractions import Fraction
import collections
from itertools import permutations
from collections import defaultdict
from collections import deque
from collections import Counter
import threading
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')

class SegmentTree:

	def __init__(self, data, default=0, func=lambda a, b: max(a, b)):
		self._default = default
		self._func = func
		self._len = len(data)
		self._size = _size = 1 << (self._len - 1).bit_length()
		self.data = [default] * (2 * _size)
		self.data[_size:_size + self._len] = data
		for i in reversed(range(_size)):
			self.data[i] = func(self.data[i + i], self.data[i + i + 1])

	def __delitem__(self, idx):
		self[idx] = self._default

	def __getitem__(self, idx):
		return self.data[idx + self._size]

	def __setitem__(self, idx, value):
		idx += self._size
		self.data[idx] = value
		idx >>= 1
		while idx:
			self.data[idx] = self._func(self.data[2 * idx], self.data[2 * idx + 1])
			idx >>= 1

	def __len__(self):
		return self._len

	def query(self, start, stop):
		if start == stop:
			return self.__getitem__(start)
		stop += 1
		start += self._size
		stop += self._size
		res = self._default
		while start < stop:
			if start & 1:
				res = self._func(res, self.data[start])
				start += 1
			if stop & 1:
				stop -= 1
				res = self._func(res, self.data[stop])
			start >>= 1
			stop >>= 1
		return res

	def __repr__(self):
		return 'SegmentTree({0})'.format(self.data)

class SegmentTree1:

	def __init__(self, data, default=0, func=lambda a, b: a + b):
		self._default = default
		self._func = func
		self._len = len(data)
		self._size = _size = 1 << (self._len - 1).bit_length()
		self.data = [default] * (2 * _size)
		self.data[_size:_size + self._len] = data
		for i in reversed(range(_size)):
			self.data[i] = func(self.data[i + i], self.data[i + i + 1])

	def __delitem__(self, idx):
		self[idx] = self._default

	def __getitem__(self, idx):
		return self.data[idx + self._size]

	def __setitem__(self, idx, value):
		idx += self._size
		self.data[idx] = value
		idx >>= 1
		while idx:
			self.data[idx] = self._func(self.data[2 * idx], self.data[2 * idx + 1])
			idx >>= 1

	def __len__(self):
		return self._len

	def query(self, start, stop):
		if start == stop:
			return self.__getitem__(start)
		stop += 1
		start += self._size
		stop += self._size
		res = self._default
		while start < stop:
			if start & 1:
				res = self._func(res, self.data[start])
				start += 1
			if stop & 1:
				stop -= 1
				res = self._func(res, self.data[stop])
			start >>= 1
			stop >>= 1
		return res

	def __repr__(self):
		return 'SegmentTree({0})'.format(self.data)
MOD = 10 ** 9 + 7

class Factorial:

	def __init__(self, MOD):
		self.MOD = MOD
		self.factorials = [1, 1]
		self.invModulos = [0, 1]
		self.invFactorial_ = [1, 1]

	def calc(self, n):
		if n <= -1:
			print('Invalid argument to calculate n!')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		if n < len(self.factorials):
			return self.factorials[n]
		nextArr = [0] * (n + 1 - len(self.factorials))
		initialI = len(self.factorials)
		prev = self.factorials[-1]
		m = self.MOD
		for i in range(initialI, n + 1):
			prev = nextArr[i - initialI] = prev * i % m
		self.factorials += nextArr
		return self.factorials[n]

	def inv(self, n):
		if n <= -1:
			print('Invalid argument to calculate n^(-1)')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		p = self.MOD
		pi = n % p
		if pi < len(self.invModulos):
			return self.invModulos[pi]
		nextArr = [0] * (n + 1 - len(self.invModulos))
		initialI = len(self.invModulos)
		for i in range(initialI, min(p, n + 1)):
			next = -self.invModulos[p % i] * (p // i) % p
			self.invModulos.append(next)
		return self.invModulos[pi]

	def invFactorial(self, n):
		if n <= -1:
			print('Invalid argument to calculate (n^(-1))!')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		if n < len(self.invFactorial_):
			return self.invFactorial_[n]
		self.inv(n)
		nextArr = [0] * (n + 1 - len(self.invFactorial_))
		initialI = len(self.invFactorial_)
		prev = self.invFactorial_[-1]
		p = self.MOD
		for i in range(initialI, n + 1):
			prev = nextArr[i - initialI] = prev * self.invModulos[i % p] % p
		self.invFactorial_ += nextArr
		return self.invFactorial_[n]

class Combination:

	def __init__(self, MOD):
		self.MOD = MOD
		self.factorial = Factorial(MOD)

	def ncr(self, n, k):
		if k < 0 or n < k:
			return 0
		k = min(k, n - k)
		f = self.factorial
		return f.calc(n) * f.invFactorial(max(n - k, k)) * f.invFactorial(min(k, n - k)) % self.MOD
mod = 10 ** 9 + 7
omod = 998244353
prime = [True for i in range(10001)]
prime[0] = prime[1] = False

def SieveOfEratosthenes(n=10000):
	p = 2
	c = 0
	while p <= n:
		if prime[p] == True:
			c += 1
			for i in range(p, n + 1, p):
				prime[i] = False
		p += 1

class DSU:

	def __init__(self, R, C):
		self.par = range(R * C + 1)
		self.rnk = [0] * (R * C + 1)
		self.sz = [1] * (R * C + 1)

	def find(self, x):
		if self.par[x] != x:
			self.par[x] = self.find(self.par[x])
		return self.par[x]

	def union(self, x, y):
		(xr, yr) = (self.find(x), self.find(y))
		if xr == yr:
			return
		if self.rnk[xr] < self.rnk[yr]:
			(xr, yr) = (yr, xr)
		if self.rnk[xr] == self.rnk[yr]:
			self.rnk[xr] += 1
		self.par[yr] = xr
		self.sz[xr] += self.sz[yr]

	def size(self, x):
		return self.sz[self.find(x)]

	def top(self):
		return self.size(len(self.sz) - 1) - 1

class LazySegTree:

	def __init__(self, _op, _e, _mapping, _composition, _id, v):

		def set(p, x):
			assert 0 <= p < _n
			p += _size
			for i in range(_log, 0, -1):
				_push(p >> i)
			_d[p] = x
			for i in range(1, _log + 1):
				_update(p >> i)

		def get(p):
			assert 0 <= p < _n
			p += _size
			for i in range(_log, 0, -1):
				_push(p >> i)
			return _d[p]

		def prod(l, r):
			assert 0 <= l <= r <= _n
			if l == r:
				return _e
			l += _size
			r += _size
			for i in range(_log, 0, -1):
				if l >> i << i != l:
					_push(l >> i)
				if r >> i << i != r:
					_push(r >> i)
			sml = _e
			smr = _e
			while l < r:
				if l & 1:
					sml = _op(sml, _d[l])
					l += 1
				if r & 1:
					r -= 1
					smr = _op(_d[r], smr)
				l >>= 1
				r >>= 1
			return _op(sml, smr)

		def apply(l, r, f):
			assert 0 <= l <= r <= _n
			if l == r:
				return
			l += _size
			r += _size
			for i in range(_log, 0, -1):
				if l >> i << i != l:
					_push(l >> i)
				if r >> i << i != r:
					_push(r - 1 >> i)
			l2 = l
			r2 = r
			while l < r:
				if l & 1:
					_all_apply(l, f)
					l += 1
				if r & 1:
					r -= 1
					_all_apply(r, f)
				l >>= 1
				r >>= 1
			l = l2
			r = r2
			for i in range(1, _log + 1):
				if l >> i << i != l:
					_update(l >> i)
				if r >> i << i != r:
					_update(r - 1 >> i)

		def _update(k):
			_d[k] = _op(_d[2 * k], _d[2 * k + 1])

		def _all_apply(k, f):
			_d[k] = _mapping(f, _d[k])
			if k < _size:
				_lz[k] = _composition(f, _lz[k])

		def _push(k):
			_all_apply(2 * k, _lz[k])
			_all_apply(2 * k + 1, _lz[k])
			_lz[k] = _id
		_n = len(v)
		_log = _n.bit_length()
		_size = 1 << _log
		_d = [_e] * (2 * _size)
		_lz = [_id] * _size
		for i in range(_n):
			_d[_size + i] = v[i]
		for i in range(_size - 1, 0, -1):
			_update(i)
		self.set = set
		self.get = get
		self.prod = prod
		self.apply = apply
MIL = 1 << 20

def makeNode(total, count):
	return total * MIL + count

def getTotal(node):
	return math.floor(node / MIL)

def getCount(node):
	return node - getTotal(node) * MIL
nodeIdentity = makeNode(0.0, 0.0)

def nodeOp(node1, node2):
	return node1 + node2
	return makeNode(getTotal(node1) + getTotal(node2), getCount(node1) + getCount(node2))
identityMapping = -1

def mapping(tag, node):
	if tag == identityMapping:
		return node
	count = getCount(node)
	return makeNode(tag * count, count)

def composition(mapping1, mapping2):
	return mapping1 if mapping1 != identityMapping else mapping2

def memodict(f):

	class memodict(dict):

		def __missing__(self, key):
			ret = self[key] = f(key)
			return ret
	return memodict().__getitem__

def pollard_rho(n):
	if n & 1 == 0:
		return 2
	if n % 3 == 0:
		return 3
	s = (n - 1 & 1 - n).bit_length() - 1
	d = n >> s
	for a in [2, 325, 9375, 28178, 450775, 9780504, 1795265022]:
		p = pow(a, d, n)
		if p == 1 or p == n - 1 or a % n == 0:
			continue
		for _ in range(s):
			prev = p
			p = p * p % n
			if p == 1:
				return math.gcd(prev - 1, n)
			if p == n - 1:
				break
		else:
			for i in range(2, n):
				(x, y) = (i, (i * i + 1) % n)
				f = math.gcd(abs(x - y), n)
				while f == 1:
					(x, y) = ((x * x + 1) % n, (y * y + 1) % n)
					y = (y * y + 1) % n
					f = math.gcd(abs(x - y), n)
				if f != n:
					return f
	return n

@memodict
def prime_factors(n):
	if n <= 1:
		return Counter()
	f = pollard_rho(n)
	return Counter([n]) if f == n else prime_factors(f) + prime_factors(n // f)

def distinct_factors(n):
	factors = [1]
	for (p, exp) in prime_factors(n).items():
		factors += [p ** i * factor for factor in factors for i in range(1, exp + 1)]
	return factors

def all_factors(n):
	(small, large) = ([], [])
	for i in range(1, int(n ** 0.5) + 1, 2 if n & 1 else 1):
		if not n % i:
			small.append(i)
			large.append(n // i)
	if small[-1] == large[-1]:
		large.pop()
	large.reverse()
	small.extend(large)
	return small

def binarySearch(arr, n, i, key):
	left = 0
	right = n - 1
	mid = 0
	res = n
	while left <= right:
		mid = (right + left) // 2
		if arr[mid][i] > key:
			res = mid
			right = mid - 1
		else:
			left = mid + 1
	return res

def binarySearch1(arr, n, i, key):
	left = 0
	right = n - 1
	mid = 0
	res = -1
	while left <= right:
		mid = (right + left) // 2
		if arr[mid][i] > key:
			right = mid - 1
		else:
			res = mid
			left = mid + 1
	return res
t = 1
t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	ch = 1
	res = [['' for j in range(m)] for i in range(n)]
	char = [chr(i) for i in range(97, 123)]
	char = set(char)
	if n % 2:
		if k < m // 2:
			ch = 0
		else:
			k -= m // 2
			if k % 2:
				ch = 0
		for i in range(1, m, 2):
			done = set()
			if i - 2 >= 0:
				done.add(res[0][i - 2])
			for j in char:
				if j not in done:
					res[0][i] = res[0][i - 1] = j
					break
	else:
		if k % 2:
			ch = 0
		if m % 2 and n * m - 2 * k < n:
			ch = 0
	if ch:
		print('YES')
		(i, j) = (n % 2, 1)
		for ct in range(k // 2):
			if j >= m:
				j = 1
				i += 2
			done = set()
			if j - 2 >= 0:
				done.add(res[i][j - 2])
				done.add(res[i + 1][j - 2])
			if i - 1 >= 0:
				done.add(res[i - 1][j])
				done.add(res[i - 1][j - 1])
			for x in char:
				if x not in done:
					res[i][j] = res[i][j - 1] = x
					done.add(x)
					break
			for x in char:
				if x not in done:
					res[i + 1][j] = res[i + 1][j - 1] = x
					done.add(x)
					break
			j += 2
		for i in range(n):
			for j in range(m):
				done = set()
				if res[i][j] == '':
					if j - 1 >= 0:
						done.add(res[i][j - 1])
						done.add(res[i + 1][j - 1])
					if i - 1 >= 0:
						done.add(res[i - 1][j])
					for x in char:
						if x not in done:
							res[i][j] = res[i + 1][j] = x
							break
		for i in res:
			print(*i, sep='')
	else:
		print('NO')


from string import ascii_lowercase
T = int(input())
for _ in range(T):
	(n, m, k) = map(int, input().split())
	swap = False
	if m % 2 == 1:
		(n, m, k) = (m, n, n * m // 2 - k)
		swap = True
	D = list(ascii_lowercase * 10000)
	if n % 2 == 0:
		flag = k % 2 == 0
	else:
		k -= m // 2
		flag = k >= 0 and k % 2 == 0
		k += m // 2
	v = n * m // 2 - k
	if flag:
		M = [[None] * m for _ in range(n)]
		(r, c) = (0, 0)
		if n % 2 == 1:
			for i in range(m // 2):
				e = D.pop()
				M[0][2 * i] = M[0][2 * i + 1] = e
				k -= 1
			(r, c) = (1, 0)
		while k > 0:
			e = D.pop()
			if r != 0:
				while e == M[r - 1][c] or e == M[r - 1][c + 1]:
					e = D.pop()
			M[r][c] = M[r][c + 1] = e
			e = D.pop()
			if r != 0:
				while e == M[r][c] or e == M[r][c + 1]:
					e = D.pop()
			M[r + 1][c] = M[r + 1][c + 1] = e
			c += 2
			k -= 2
			if c == m:
				r += 2
				c = 0
		while v > 0:
			e = D.pop()
			if r != 0:
				while e == M[r - 1][c]:
					e = D.pop()
			M[r][c] = M[r + 1][c] = e
			e = D.pop()
			if r != 0:
				while e == M[r - 1][c + 1]:
					e = D.pop()
			M[r][c + 1] = M[r + 1][c + 1] = e
			c += 2
			v -= 2
			if c == m:
				r += 2
				c = 0
	print('YES' if flag else 'NO')
	if flag:
		if swap:
			M = [[M[r][c] for r in range(n)] for c in range(m)]
		for r in M:
			print(''.join(r))


for _ in range(int(input())):
	(n, m, k) = map(int, input().split())
	(hr, vr) = (k, m * n // 2 - k)
	four = n // 2 * (m // 2)
	mat = [[0 for i in range(m)] for j in range(n)]
	ans = 'YES'
	if m % 2 == 0:
		if n % 2 != 0:
			hr -= m // 2
			for i in range(0, m, 2):
				if i == 0 or mat[-1][i - 1] == 'b':
					mat[-1][i] = 'a'
					mat[-1][i + 1] = 'a'
				else:
					mat[-1][i] = 'b'
					mat[-1][i + 1] = 'b'
	elif n % 2 == 0:
		vr -= n // 2
		for i in range(0, n, 2):
			if i == 0 or mat[i - 1][-1] == 'c':
				mat[i][-1] = 'd'
				mat[i + 1][-1] = 'd'
			else:
				mat[i][-1] = 'c'
				mat[i + 1][-1] = 'c'
	if vr >= 0 and hr >= 0:
		if hr % 2 != 0:
			ans = 'NO'
	else:
		ans = 'NO'
	if ans == 'YES':
		print(ans)
		for i in range(0, n - n % 2, 2):
			for j in range(0, m - m % 2, 2):
				if hr != 0:
					if j == 0 or mat[i][j - 1] != 'e':
						mat[i][j] = 'e'
						mat[i][j + 1] = 'e'
						mat[i + 1][j] = 'f'
						mat[i + 1][j + 1] = 'f'
					else:
						mat[i][j] = 'g'
						mat[i][j + 1] = 'g'
						mat[i + 1][j] = 'h'
						mat[i + 1][j + 1] = 'h'
					hr -= 2
				else:
					if i == 0 or mat[i - 1][j] != 'i':
						mat[i][j] = 'i'
						mat[i + 1][j] = 'i'
						mat[i][j + 1] = 'j'
						mat[i + 1][j + 1] = 'j'
					else:
						mat[i][j] = 'k'
						mat[i + 1][j] = 'k'
						mat[i][j + 1] = 'l'
						mat[i + 1][j + 1] = 'l'
					vr -= 2
		for i in range(n):
			for j in range(m):
				print(mat[i][j], end='')
			print('')
	else:
		print(ans)


from sys import stdin, stdout
input = stdin.readline
import random
t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	change = 0
	if m % 2:
		change = 1
		(n, m) = (m, n)
		k = n * m // 2 - k
	vv = m * (n // 2)
	hh = 0
	if n % 2:
		hh = m // 2
	ans = 'no'
	assert vv % 2 == 0
	mat = [['' for i in range(m)] for j in range(n)]
	val = 97
	arr = [chr(i) for i in range(97, 97 + 26)]
	brr = arr.copy()
	for i in range(0, 26, 2):
		(brr[i], brr[i + 1]) = (brr[i + 1], brr[i])
	kk = -1
	for i in range(0, n, 2):
		kk += 1
		val = -1
		if i == n - 1:
			last = -1
			for j in range(0, m, 2):
				block = [last]
				if i - 1 >= 0:
					block.append(ord(mat[i - 1][j]))
					block.append(ord(mat[i - 1][j + 1]))
				while 1:
					ran = random.randint(97, 97 + 25)
					if ran not in block:
						break
				mat[i][j] = chr(ran)
				mat[i][j + 1] = chr(ran)
				last = ran
			continue
		for j in range(m):
			val += 1
			if val == 26:
				val = 0
			if kk % 2:
				mat[i][j] = brr[val]
				mat[i + 1][j] = brr[val]
			else:
				mat[i][j] = arr[val]
				mat[i + 1][j] = arr[val]
	r = 0
	c = 0
	while 1:
		if hh == k:
			ans = 'yes'
			break
		if vv == 0:
			break
		hh += 2
		vv -= 2
		block = set()
		if r - 1 >= 0:
			block.add(ord(mat[r - 1][c]))
			block.add(ord(mat[r - 1][c + 1]))
		if r + 2 < n:
			block.add(ord(mat[r + 2][c]))
			block.add(ord(mat[r + 2][c + 1]))
		if c - 1 >= 0:
			block.add(ord(mat[r][c - 1]))
			block.add(ord(mat[r + 1][c - 1]))
		if c + 2 < m:
			block.add(ord(mat[r][c + 2]))
			block.add(ord(mat[r + 1][c + 2]))
		while 1:
			ran = random.randint(97, 97 + 25)
			if ran not in block:
				block.add(ran)
				mat[r][c] = chr(ran)
				mat[r][c + 1] = chr(ran)
				break
		while 1:
			ran = random.randint(97, 97 + 25)
			if ran not in block:
				block.add(ran)
				mat[r + 1][c] = chr(ran)
				mat[r + 1][c + 1] = chr(ran)
				break
		if hh == k:
			ans = 'yes'
			break
		c += 2
		if c >= m:
			c = 0
			r += 2
	print(ans.upper())
	if ans == 'no':
		continue
	if change:
		mat2 = [['' for i in range(n)] for j in range(m)]
		for i in range(n):
			for j in range(m):
				mat2[j][i] = mat[i][j]
		mat = mat2
	for i in mat:
		print(''.join(i))


t = int(input())
for _ in range(t):
	(n, m, k) = map(int, input().split())
	ans = [[0 for i in range(m)] for j in range(n)]
	if n % 2 == 1:
		c = n * m // 2 - k
		if 0 <= c <= (n - 1) * m // 2 and c % 2 == 0:
			print('YES')
			i = 0
			j = 0
			done = 0
			if c != 0:
				for i in range(0, n, 2):
					for j in range(m):
						ans[i][j] = chr((j + i // 2) % 2 + 97)
						ans[i + 1][j] = chr((j + i // 2) % 2 + 97)
						c = c - 1
						if c == 0:
							j = (j + 1) % m
							done = 1
							break
					if done == 1:
						break
			if j != 0:
				for d in range(j, m, 2):
					ans[i][d] = chr((d // 2 + i) % 2 + 99)
					ans[i][d + 1] = chr((d // 2 + i) % 2 + 99)
				i = i + 1
				for d in range(j, m, 2):
					ans[i][d] = chr((d // 2 + i) % 2 + 99)
					ans[i][d + 1] = chr((d // 2 + i) % 2 + 99)
				i = i + 1
			elif done == 1:
				i = i + 2
			for e in range(i, n):
				for f in range(0, m, 2):
					ans[e][f] = chr((f // 2 + e) % 2 + 101)
					ans[e][f + 1] = chr((f // 2 + e) % 2 + 101)
			for aa in ans:
				print(''.join(aa))
		else:
			print('NO')
	elif m % 2 == 1:
		if 0 <= k <= (m - 1) * n // 2 and k % 2 == 0:
			print('YES')
			i = 0
			j = 0
			done = 0
			if k != 0:
				for j in range(0, m, 2):
					for i in range(n):
						ans[i][j] = chr((j // 2 + i) % 2 + 97)
						ans[i][j + 1] = chr((j // 2 + i) % 2 + 97)
						k = k - 1
						if k == 0:
							i = (i + 1) % n
							done = 1
							break
					if done == 1:
						break
			if i != 0:
				for d in range(i, n, 2):
					ans[d][j] = chr((j + d // 2) % 2 + 99)
					ans[d + 1][j] = chr((j + d // 2) % 2 + 99)
				j = j + 1
				for d in range(i, n, 2):
					ans[d][j] = chr((j + d // 2) % 2 + 99)
					ans[d + 1][j] = chr((j + d // 2) % 2 + 99)
				j = j + 1
			elif done == 1:
				j = j + 2
			for e in range(j, m):
				for f in range(0, n, 2):
					ans[f][e] = chr((f // 2 + e) % 2 + 101)
					ans[f + 1][e] = chr((f // 2 + e) % 2 + 101)
			for aa in ans:
				print(''.join(aa))
		else:
			print('NO')
	elif 0 <= k <= n * m // 2 and k % 2 == 0:
		print('YES')
		i = 0
		j = 0
		done = 0
		if k != 0:
			for j in range(0, m, 2):
				for i in range(n):
					ans[i][j] = chr((j // 2 + i) % 2 + 97)
					ans[i][j + 1] = chr((j // 2 + i) % 2 + 97)
					k = k - 1
					if k == 0:
						i = (i + 1) % n
						done = 1
						break
				if done == 1:
					break
		if i != 0:
			for d in range(i, n, 2):
				ans[d][j] = chr((j + d // 2) % 2 + 99)
				ans[d + 1][j] = chr((j + d // 2) % 2 + 99)
			j = j + 1
			for d in range(i, n, 2):
				ans[d][j] = chr((j + d // 2) % 2 + 99)
				ans[d + 1][j] = chr((j + d // 2) % 2 + 99)
			j = j + 1
		elif done == 1:
			j = j + 2
		for e in range(j, m):
			for f in range(0, n, 2):
				ans[f][e] = chr((f // 2 + e) % 2 + 101)
				ans[f + 1][e] = chr((f // 2 + e) % 2 + 101)
		for aa in ans:
			print(''.join(aa))
	else:
		print('NO')