题目内容：

听下面一段独白，回答以下小题。

1.When do wisdom teeth usually start to appear?

A. In one’s childhood. B. In one’s middle age. C. In one’s early twenties.

2.When may a wisdom tooth cause a problem?

A. When there is too much gum (齿龈) around it.

B. When there is not enough room for it to grow.

C. When it completely rises through the gum.

3.What does the American Dental Association suggest doing when a wisdom tooth appears?

A. Removing it. B. Brushing it regularly. C. Eating soft food.

4.Why do people have wisdom teeth according to scientists?

A. People still need them for chewing.

B. People need them to protect their gums.

C. Ancient humans needed extra chewing teeth.