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1、大学英语语法讲解情态动词的完成时(表示对过去的说法)must+have+过去分词（用于肯定句）一定已经…….Thelightisstillon.Theymusthaveforgottentoturnitoffwhentheylefttheroom.注:mustn’thavedone×can’t(couldn’t)+have+过去分词（用于否定或疑问句）不可能……..HecannothavebeentothattownforIsawhimjustnow.should/oughtto+have+过去分词本应该做(却没有做)…….Ashisb
2、estfriend,youshould/oughttohavehelpedhim.(butinfact,youdidn’t.)shouldn’t/oughtnotto+have+过去分词本不应该做(却做了)…….Youshouldn’thaveparkedyourcarhere,forit’sapublicplace.needn’t+have+过去分词本不必做……Youneedn’thavewaitedforme.ItoldyouyesterdayIwouldoverwork.withwith+doneWiththehomeworkfi
3、nished,theboywentout.with+doingWiththeoldmanleadingtheway,wefinallyfindthehouse.with+prepWiththelighton,allthestudentswentoutoftheclassroom.虚拟语气的用法概念：表示说话人的愿望、假设、猜测、或建议，而不表示客观存在的事实。虚拟语气通过谓语动词的特殊形式来表示虚拟语气用于条件状语从句(1)与过去事实相反If…had+done,…would(should,could,might)+have+doneIf
4、youhadtakenmyadvice,youwouldn’thavefailedintheexam.与现在事实相反If+did(be→were)，…would(should,could,might)+doIfhehadtime,hewouldattendthemeeting.IfIwereyou,IshouldstudyEnglish.与将来事实相反If+did(be—were)/wereto/should+do,…would(should,could,might)+doIfyoucametomorrow,wewouldhavethe
5、meeting.Ifitweretoraintomorrow,themeetingwouldbeputoff.虚拟语气用于宾语从句在表示建议、要求、命令类的动词后面的宾语从句中用(should)+do。如:advise,suggest,propose,request,require,insist,demand,order,command,desireWesuggestedthatwe(should)haveameeting.Weinsistedthatthemeeting(should)becancelled.注意：suggest作“暗
6、示，表明”解时，insist作“坚决认为”解时不用虚拟语气，而用一般的时态。Mikeinsistedthathehadneverstolenanything.Hersun-tannedfacesuggestedthatshewasinexcellenthealth.虚拟语气用于主语从句Itisnecessary(important,natural,strange,essential,etc.)thatsb(should)+动词原形Thisisaverydifficultoperation.Itisessentialthatyoubepr
7、eparedforemergency.Itisbesuggested(desired,ordered,proposed,advised,etc.)thatsb(should)+do虚拟语气用于表语从句、同位语从句作advice,idea,order,demand,plan,proposal,suggestion,request，wish等名词的表语从句、同位语从句。其谓语动词用(should)+动词原形Weallagreedtohissuggestionthatwe(should)gotoBeijingforsightseeing.it
8、is(high)timesb+didItis(high)timeweleft.虚拟语气用于ifonly引导的感叹句中(要是…就好了)IfonlyIhadtakenhisadvice.accountfor:解
