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:
['y', 'g', '107', '4899', '6357', '9777', 'k', '1865', '7029', 'q', 'x', '7051', 's', '6125', '4285', '2731', 'z', 'a', '737', '6137']
answer:
a, g, k, q, s, x, y, z


question:
['m', '6443', 'd', 'o', 'p', 'q', '3765', 'k', 'm', 'y', 'j', '3531', 'y', 't', '671', 'j', '3699', 'a', 'i', '1843', 't', 'd', '1205', 'k', 'h', '1209', '2913', '1301', 'k', 'd', '1769', '7985', 's', 'p', 'f', '4583']
answer:
a, d, f, h, i, j, k, m, o, p, q, s, t, y


question:
['n', '4569', 'e', '9835', 'g', 'u', 'g', 't', '8995', 'j', '9', '2365', '5783', 't', 'b', '7341', 'u', 'k', 'c', 'f', 'o', '9053', 'n', '5797', '5899', 'b', '5265', '2487', '6023', 'k', 'o', 'e', '4351', '1781', '3033', '1369', 'a', 'd', 'b', '3709', 'y']
answer:

a, b, c, d, e, f, g, j, k, n, o, t, u, y