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:
['w', 'n', '729', '2491', 'n', 'x', '915', '1869', 'z', '8491', '9947', '561', '829', 'n', 't', 'i']
answer:
i, n, t, w, x, z


question:
['m', '6537', '4063', '6413', 'k', 'd', '2479', 'p', '2251', 'q', '7079', 'r', 'd', 'p', '3347', '1391', '9847', '4487', 'u', '6951', '5285', '5837', '6747', 'r', 's', 'c', 'x', 'b', 'q', 'y', 'd', '331', '679', 'v', '1919', 'f', 'p', '1267', '3151']
answer:
b, c, d, f, k, m, p, q, r, s, u, v, x, y


question:
['r', '9105', '3777', '859', '7839', 'r', 'p', '6635', '6795', 'u', '8667', '8667', '15', 'e', '9317', '543', 'j', '9985', 't', 'b', '347', '359', 'y', 'm', 's', '6069', '3525']
answer:

b, e, j, m, p, r, s, t, u, y