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: ['a', 'o', 'g', 't', '8667', '1207', 'v', '4651', '3205', '3349', 'a', '2245', '3693', 'g', '6531', '7567', '999', 'i', '6895', '2685', '6835', 'w', '2129', 't', '6817', 't', '907', 'u', '1849', '7683', '2663']
Student:
a, g, i, o, t, u, v, w