input: Write a python function to return all the words in a string in alphabetical order.
  assert sort_words("hello world this is a test") == ['a', 'hello', 'is', 'test', 'this', 'world']
  assert sort_words("banana apple kiwi") == ['apple', 'banana', 'kiwi']
  assert sort_words("quick brown fox jumps over the lazy dog") == ['brown', 'dog', 'fox', 'jumps', 'lazy', 'over', 'quick', 'the']
output: def sort_words(s):
      words = s.split()
      words.sort()
      return words