input: Below is an instruction that describes a task. Write a response that appropriately completes the request.
  
  ### Instruction:
  Generate a Python program that takes a sentence as input and prints out only the verbs.
  
  ### Input:
  The cat jumped over the moon.
  
  ### Output:
  import nltk
  
  def extract_verbs(sentence):
      """ Takes a sentence as input and returns a list of verbs.
      >>> extract_verbs("The cat jumped over the moon.")
      ['jumped']
      """
      tokens = nltk.word_tokenize(sentence)
      tags = nltk.pos_tag(tokens)
      verbs = [word for word, pos in tags if pos.startswith('V')]
      return verbs
output:     return [word for word, pos in tags if pos.startswith('V')]