input: Write a python function to authenticate to the Twitter API using Tweepy and return an API object.
  assert isinstance(authenticate_twitter('your_consumer_key', 'your_consumer_secret', 'your_access_token', 'your_access_token_secret'), tweepy.API)
  assert authenticate_twitter('invalid_key', 'invalid_secret', 'invalid_token', 'invalid_token_secret') is None
output: def authenticate_twitter(consumer_key, consumer_secret, access_token, access_token_secret):
      import tweepy
      try:
          auth = tweepy.OAuth1UserHandler(consumer_key, consumer_secret, access_token, access_token_secret)
          api = tweepy.API(auth)
          api.verify_credentials()
          return api
      except:
          return None