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题型:阅读理解-单选 难度:0.65 引用次数:50 题号:21940082

Why Do We Yawn?


Do you yawn? There are about 20 reasons that scientists think are possible for yawning after research. They do not know exactly why yawning happens, but they do know many facts about yawning.

We know that everyone yawns in the same way. First you open your mouth slowly. Your mouth stays open for about five seconds. You take in a lot of air and then push it out. Then you quickly close your mouth. We also know that yawning is contagious. When you see someone yawn, you yawn, too.

Many people say they yawn because they are bored or tired. That might be true. People do often yawn before they sleep and after they wake up. However, we know that people also yawn when they are excited or nervous. Olympic runners, for example, scientists found that a yawn can help a warm brain cool down.

Some scientists believe that yawning makes you notice things more quickly. When you yawn, you breathe deeply. You also stretch (强化) the muscles (肌肉), mouth, and neck. Your eardrums stretch, too. Maybe this helps you to be quicker to notice things.

In some countries, people think yawning is not nice. People put their hands over their mouths to cover a yawn. In other countries, people think yawning is healthy. They think that opening the mouth very big can let good things in. When they breathe out, they think that bad things go out of the body with the air.

Scientists do not spend much time studying yawning. That is probably because yawning does not hurt. It is just something we do.

1. What does the underlined word “contagious” in Paragraph 2 mean?
A.Able to spread quickly.
B.Able to breathe easily.
C.Able to change easily.
D.Able to sleep quickly.
2. Why do Olympic runners often yawn before a race?
A.They are too tired or too bored.
B.A yawn can let good things in.
C.A yawn can help a warm brain cool down.
D.A yawn can stretch the muscles in their faces.
3. What is the main idea of Paragraph 5?
A.Reasons for yawning.
B.Advantages of yawning.
C.Disadvantages of yawning.
D.Different ideas about yawning.
4. What would be the best structure of the passage?
A.B.C.D.
【知识点】 科普知识 说明文

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