The word "nomadic" in the sentence "How is this affected by whether a bird is nomadic." can best probably mean ______.

A．It comes about perhaps because of the change of their DNA.
B．It comes about simply due to imitation of the other birds' manner.
C．Because the birds have learned the local dialect by learning the local dialect from generation to generation.
D．Both A and

A．whales are as constantly changing their song as birds, creating what is known
B．whales are seldom changing their song in the way we find in birds
C．birds are less often changing their songs than whales are
D．birds would never change their songs as whales would do