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 powerful and versatile programming language.")
      "programming"
      """
output:     words = sentence.split()
      longest_word = ""
      for word in words:
          if len(word) > len(longest_word):
              longest_word = word
      return longest_word