Teacher: 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.
Teacher: Now, understand the problem? If you are still confused, see the following example:
['8129', 'a', '4245', 'y', 'm', 'a']
Solution: a, m, y
Reason: Here, the unique alphabets in the list are 'a', 'y', and 'm', hence their sorted order is 'a, m, y'.

Now, solve this instance: ['73', 'l', 'g', '221', 'q', '6011', '1001', '539', 'h', 'z', '7777', 'p', 't', 'v', 'y', 'o', 'o', '4839', '2317', 'k', '7613', 'f', '5985']
Student:
f, g, h, k, l, o, p, q, t, v, y, z