input: def find_longest_word(sentence: str) -> str:
      """ Identify the longest word in a given sentence.
      >>> find_longest_word("The rain in Spain stays mainly in the plain.")
      'mainly'
      >>> find_longest_word("Python is a very powerful language.")
      'powerful'
      """
output:     words = sentence.split()
      longest_word = max(words, key=len)
      return longest_word