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:
['3147', '9807', '5313', '6311', '737', '1555', '5803', '3437', '5665', '3973', 'o', 'f', '7871', '1721', '7833', '2933', 'b', 'b', 'n', 'm', 'k']
answer:
b, f, k, m, n, o


question:
['2505', '4199', 'e', '5433', '8795', 'q', 'i', '9357', 'o', '257', '8235', 'b', '1339', 'w', '1463', 'm', '277', '3211', '3863', 'r', 'm', 'i', '5793', '7451', '4787', '4739', 'k', 't', 'o', '7453', '9385', 'v', 'l', 'y', 'f', 'r', 'p', 'w']
answer:
b, e, f, i, k, l, m, o, p, q, r, t, v, w, y


question:
['t', '6881', 'e', 'z', 'u', 't', '2517', 'u', '5077', '4567', '2787', '5031', '3647', '1441', 'j', '3267', 'u', 'u', 'y', '6907']
answer:

e, j, t, u, y, z