[单项选择]One language is used in every country. People, young and old, short and tall, thin and fat, use it very often. It’s everybody’s second language. It is easy to understand. It is the sign language.
When you wave your hand in the street, you are saying "Hello" to your friend. When you put up your hand in class, you’re telling the teacher that you know the fight answer or that you want to ask your teacher a question. When a policeman wants to stop cars or buses, he raises his hand. He is using sign language.
Sign language is more useful in quiet places. For example, when you are swimming with your friends, you can have a talk under water by using sign language.

A policeman stop a car by blowing his whistle.
A. Right.
B. Wrong.
C. Doesn’t say.