21（）

A．he liked to live alone
B．people didn’t like him and were afraid of him
C．he liked to walk in the woods without roads
D．he didn’t do anything as the others did

A．Many animals have poor eyesight while their sense of smell, is quite good.
B．Dogs are color blind.
C．The human sense of smell is not good.
D．Dogs can see no more than shades of gray.