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? Solve this instance: ['6491', '8953', 'p', 'a', 'r', '9229', '1979', 'b', '1977', 'z', '9927', '7503', '5289', '805', '5763', '2175', 'm', 'b', '2929', '8343', '4181', '7169', '2837', 'r', 'b', 's', '6481', 'h', '3629', '3', 'a', '7435', 'c', 'r', 'b', 'l', '5177', '2303', '6181', '6945', 's', '4483', '1563']
Student:
a, b, c, h, l, m, p, r, s, z