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1、GRE写作素材之打哈欠的奥秘考生想要在GRE写作中写出优秀的文章，就一定要积累较多的材和写作技巧，下面就给大家整理的一篇GRE写作素材题材，希望大家取得理想的成绩。ThemysteryofyawningAccordingtoconventionaltheory,yawning（打哈欠）takesplacewhenpeopleareboredorsleepyandservesthefunctionofincreasingalertness(机敏)byreversing,throughdeeperbreathing,thedropinbloodoxygenlevelsthatarecau
2、sedbytheshallowbreathingthataccompanieslackofsleeporboredom.Unfortunately,thefewscientificinvestigationsofyawninghavefailedtofindanyconnectionbetweenhowoftensomeoneyawnsandhowmuchsleeptheyhavehadorhowtiredtheyare.Abouttheclosestanyresearchhascometosupportingthetirednesstheoryistoconfirmthatadul
3、tsyawnmoreoftenonweekdaysthanatweekends,andthatschoolchildrenyawnmorefrequentlyintheirfirstyearatprimaryschoolthantheydoinkindergarten.根据传统理论，当人们无聊或者困倦时就会打哈欠。伴随睡眠不足或无聊的是浅呼吸，而浅呼吸会降低血液中氧的含量。打哈欠可以通过深呼吸逆转这一点，增加血液中氧的含量从而达到提高警觉性的功能。但遗憾的是，少量关于打哈欠的科学研究并没有找到任何打哈欠频率与个人睡眠时长或者疲劳程度之间的联系。最近所有用于支持疲劳理论的研究是为了确认
4、成人在工作日比在周末打哈欠的频率更高；学生在小学一年级比在幼儿园时打哈欠的频率要高。Anotherflaw（瑕疵）ofthetirednesstheoryisthatyawningdoesnotraisealertnessorphysiologicalactivity,asthetheorywouldpredict.Whenresearchersmeasuredtheheartrate,muscletensionandskinconductance（皮肤电传导）ofpeoplebefore,duringandafteryawning,theydiddetectsomechangesi
5、nskinconductancefollowingyawning,indicatingaslightincreaseinphysiologicalactivity（生理活性）.However,similarchangesoccurredwhenthesubjectswereaskedsimplytoopentheirmouthsortobreathedeeply.Yawningdidnothingspecialtotheirstateofphysiologicalactivity.Experimentshavealsocastseriousdoubtonthebeliefthatya
6、wningistriggeredbyadropinbloodoxygenorariseinbloodcarbondioxide.Volunteersweretoldtothinkaboutyawningwhiletheybreathedeithernormalair,pureoxygen,oranairmixturewithanabove-normallevelofcarbondioxide.Ifthetheorywascorrect,breathingairwithextracarbondioxideshouldhavetriggeredyawning,whilebreathing
7、pureoxygenshouldhavesuppressedyawning.Infact,neitherconditionmadeanydifferencetothefrequencyofyawning,whichremainedconstantatabout24yawnsperhour.Anotherexperimentdemonstratedthatphysicalexercise,whichwassufficientlyvigorous（精力充沛的）
