input: Write a function to extract verbs from a given sentence and print them out. The function should use the nltk library to tokenize the sentence and tag the parts of speech, then filter out only the verbs based on their POS tags.
  assert extract_verbs("The cat jumped over the moon.")==['jumped']
  assert extract_verbs("She is running and laughing.")==['is', 'running', 'laughing']
  assert extract_verbs("He writes code every day.")==['writes', 'code']
  assert extract_verbs("They went to the store.")==['went']
  assert extract_verbs("There is no verb in this sentence.")==[]
output: def extract_verbs(sentence):
      from nltk import word_tokenize, pos_tag
      tokens = word_tokenize(sentence)
      tagged = pos_tag(tokens)
      verbs = [word for word, pos in tagged if pos.startswith('VB')]
      return verbs