According to research, people are more likely to yawn at higher temperatures. When they yawn, the act of stretching their jaws sends more blood to their brain, which can help keep it cool. Also, taking in a big breath of air during a yawn ensures a minor increase in blood flow to the brain. Another theory proposes that yawning is a survival mechanism that increases people’s level of alertness. If someone is getting drowsy and their awareness begins to decrease, yawning may be triggered to keep them from falling asleep.
根據研究，人們在高溫下較有可能打哈欠。當他們打哈欠，伸展下巴的動作會讓更多血液流向大腦，這可以幫助它保持冷卻。此外，打哈欠時吸進大口空氣能確保輸往大腦的血流略為增加。另一項理論指出打哈欠是增加人們警覺性的生存機制。如果某人變得昏昏欲睡且意識開始消退，打哈欠或許會被啟動來防止其睡著。
生活必備字詞：
yawn n. & vi.（打）哈欠
drowsy a. 昏昏欲睡的
keep... from V-ing 使……免於……
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本文節錄自《常春藤生活英語》雜誌，完整內容請見七月號。
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