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十万个为什么·科学阅读30篇(8)

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Why Do We Yawn?

Why Do We Yawn?

人为什么会打哈欠?

  1. Yawning happens when we feel tired or bored.
  2. It may help cool down our brain and body.
  3. We take a big breath, then stretch our jaw wide.
  4. More oxygen enters our lungs and blood.
  5. Some scientists think yawning helps us stay alert.
  6. It also spreads easily — seeing others yawn makes us yawn too.
  7. Even babies yawn before they are born.
  8. Yawning is natural and nothing to worry about.
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