题目内容：
听音频，回答题 Thereisaneffectthatnotonlyhaveweallwitnessed,buthave26.Haven'tweallbeenonanelevatorandnoticedthatjustabouteveryonestopstalkingwhentheygeton?Whydowedothat?Youcanbehavinga27pleasantconversationwithsomeone,andassoonasyougetonanelevator,youjustfeellikeyou'dbettershutup.
Then,assoonasthedoorsopen,everyone28conversation.Primatologists,orpeoplewhostudyprimate(灵长类动物)behavior,haveatermforthis.It'scalledthe"elevatoreffect,"thoughitdoesn't29onlyonelevators.Ithappenswheneveragroupofprimates,likehumans,is30asituationwhereescapeis31impossible.It'sthoughttobeakindofsafety32:aslongasnobodytalks,nobodyisgoingtoriskgettinginafightwhenthere'snowaytospreadout.Theelevatoreffectkeepsalidonpotentialproblemsbeforetheystart.
Eventhoughtheyrarelyifeverrideelevators,chimpanzeesdemonstratetheelevatoreffectaswell.Whenchimpsaretemporarilycrowdedtogetherintosmallareas,theywill33theirvocalcommunication,thatis,nobodyspeaks,andavoideye34.Theamountofscratchingthechimpsdo,however,goesup.Sincescratchingisasignofstressinchimps,wecanimaginewhattheyarefeeling.It'sjustlikewhatwefeelinacrowdedelevator--everybodycarefully35thelightednumbersandnoonesayingathing.
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