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:
['g', 'h', 'g', 'g', 's', 'h', '2849', '2705', '1185', 'x', '5789', '8221', 'e', 'x', 'g', 'b', '4903', 'q', '1563', 'r', 'k', 't', '9047', 'p', 'p', '9397', 'u', '7473', 'f', 'o', 'y', '1957', '1039', '9905', 'i', '4829', 'q', 'w', 'k', 'p', 't', '563', 'g', 'l']
answer:
b, e, f, g, h, i, k, l, o, p, q, r, s, t, u, w, x, y


question:
['6877', '6605', 'l', '2213', 'm', 'p', '445', 'l', 's', 'b', '6607', '2639', 'y', 'd', 'm', 'o', '6419', '489', 'k', '6631', '8349', '5955', '9041', '3127', 'a']
answer:

a, b, d, k, l, m, o, p, s, y