Pigeons have been known to fly as fast as _____.

A．Elephants can be graceful.
B．Tigers are too dangerous to be trained.
C．Animals which are natural enemies can be trained to live together.
D．Animals can become interested in their tricks.

A．they are following a trail of something that smells good to them
B．they are returning to their families
C．they have been trained to work with other animals
D．they do not know a movie actor is nearby