input: def reverse_words(string: str) -> str:
      """ This function takes a sentence and reverses the order of words in it while keeping the order of characters in each word unchanged.
      >>> reverse_words('keep the order of the characters')
      'characters the of order the keep'
      >>> reverse_words('This is a sentence.')
      'sentence. a is This'
      """
output:     words = string.split()
      reversed_words = words[::-1]
      return ' '.join(reversed_words)