Koalas look like teddy bears, __

Koalas look like teddy bears, ___21___ they are not bears at all. They are really animals called marsupials.
These animals carry their young in pouches, like kangaroos ___22___.Koalas live in the forests of Australia. They spend most of their lives in eucalyptus trees. They ___23___ never come down even for a drink of water. In fact, their names means “no drink.” The koalas have a ___24___ of knowing which trees they can feed on safely. They eat each leaf the same way. ___25___ , they bite the leaf off the stem and then they chew it from base to ___26___.
When a koala is born, it is less than an inch long. The baby crawls into the mother’s ___27___ right away and stays there for six months. After that, the baby rides piggyback or hangs on ___28___ the mother’s front paws and legs. Young koalas stay with their mothers for at least a year.
The koala is a strong climber. Its paws end with sharp claws, ___29___ he can get a good grip on tree branches. Koalas sleep in the eucalyptus trees on most of the day and eat at night. Koalas may live alone or in small ___30___ . Males sometimes use their sharp claws as weapons. Most of the time, koala families live together peacefully.
21.
A、while
B、but
C、when
D、however
【正确答案】：B