How Why1---Yaw讲读版

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英文原文：

Why Do We Yawn?

Bears yawn. Camels yawn. Most mammals yawn.Why do we yawn?No one really knows the answer.

We do know that / everyone yawns in the same way.First / you open your mouth slowly. Your mouthstays open /for about five seconds.Then / you quicklyclose your mouth.

We alsoknow that yawning is contagious, / or catching. When you see someone yawn, / you yawn, too. Many people say that theyyawn / because they are bored or tired. This might be true.However, we knowthat people alsoyawn / when they are excited or nervous. Olympicrunners, for example, /often yawn before a race. Why is that?

Some scientistsbelieve that / yawning makes you morealert. When you yawn, / you breathe moredeeply. You alsostretch the muscles/ in your face and neck. Maybe this makes you feel morealert.

Scientistsdon’t spend muchtime studying yawning. That is probably because / yawning doesn’t hurt. It is just something we do.