- 问题详情:Whatisayawn(哈欠)andwhydopeopleyawn?Ayawnisoftenassociatedwithapersonbeingtired.__1__Peopleyawnformanyreasonsincludingstress,boredom,emotionandoverwork.Haveyounoticedthatyawningseemstobecontagious(会传染的)?Ifonepersonyawns,thisappearstocause...
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