Yawning（打哈欠） is something we all do—— maybe because we are tired of carrying out boring tasks or because we are tired.Sometimes，just seeing other people yawn can make you excited.
    According to BBC，new research suggests it might be because yawning cools the brain down and prevents it from overheating （過熱），muck like the fun in your computer.This might be why we are more eager（渴望的）to sleep and yawn in the warm temperatures.
    We yawn more when we are tired or ready for a short rest，and we can't control when we do it!But it is also true that yawning is a very contagious（接 觸傳 染的）action.John Drury，a researcher from Sussex University，told the BBC that "It's something that you can't stop.Dogs yawn when their owners yawn，animals yawn to each other.It happens whether you want to or not."
    His research into this behavior found that there is a connection with our social group and how close we are to the people in it.If we are closely connected with the person who shows the behavior，we are likely to copy it too.
    Another research by the University of Nottingham in 2017 found similar results.They asked volunteers to watch other people yawn.They found they couldn't help yawning when others around them yawned.

Title：（1） Why Why do we yawn？
The possible （2） reasons reasons for yawning	We are tired of carrying out boring tasks or we are tired. We need to cool our brain down and prevent it from overheating.
The findings of the research	Warm temperatures may be easier for（3） sleeping sleeping and yawning. Yawning is an action that is very contagious. Yawning is something we can't（4） control control .It happens whether we want to or not.
The conclusion	There is a（5） connection connection with our social group and how close we are to the people in it.