input: Write a python function to find the longest word in a given sentence.
  assert find_longest_word("The quick brown fox jumps over the lazy dog") == "jumps"
  assert find_longest_word("A journey of a thousand miles begins with a single step") == "thousand"
  assert find_longest_word("To be or not to be that is the question") == "question"
output: def find_longest_word(sentence):
      words = sentence.split()
      longest_word = max(words, key=len)
      return longest_word