input: def extract_verbs(sentence: str) -> list:
      """
      Given a sentence, this function extracts and returns only the verbs.
  
      >>> extract_verbs("The cat jumped over the moon.")
      ['jumped']
      >>> extract_verbs("She is running fast.")
      ['is', 'running']
      >>> extract_verbs("This is a test.")
      ['is']
      """
output:     from nltk import pos_tag, word_tokenize
  
      words = word_tokenize(sentence)
      tagged_words = pos_tag(words)
      verbs = [word for word, tag in tagged_words if tag.startswith('VB')]
      return verbs