instruction:
In this task, you are given an input list A comprising of numbers and alphabets. You need to extract and sort the unique alphabets in the list. The alphabets in the input list will only be in lowercase. Return -1 if there is no alphabet in the input list.
question:
['4749', '4607', '625', '6907', 't', 'b', '8479', '6505', 'r']
answer:
b, r, t


question:
['9923', 'x', '1901', 'v', '1459', '7503', '3829', '4929', 'k', 'c', '3329', '8793', 'n', 'a', '7249', 'b', 'l', 'l', 'm', 'p', 'b', 'a']
answer:
a, b, c, k, l, m, n, p, v, x


question:
['5781', '5839', 'z', 'b', '327', 'v', '9037', 'z', '2689', '1273', 'f', 'k', 'i', '4727', 'h', 'f', 'a', 'q', '1641', 'v', 'h', 't', 'h', 'l', '1637', '9911', '6353', '1061', '7849', '6465', 'm', '3537', '6405', '699', '5597', '6527', 'z', 'k', '335', '3669', 'n', '7515', 'j', '1969']
answer:

a, b, f, h, i, j, k, l, m, n, q, t, v, z