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主语从句一、概述：在句子中起名词作用的各种从句统称为名词性从句。根据它们在句中的语法作用，这类从句又可分为主语从句、同位语从句、表语从句和宾语从句。二.主语从句主要有四类：（1）由连词that引导的主语从句:引导词that无含义/在句中不做成分/不可以省。例如：Thatyouwillwinthemedalseemsunlikely.Thatyouaresoindifferentbothersme.Thatshesurvivedtheaccidentisamiracle.（2）用连词whether引导的主语从句:whether有含义(是否)/在句中不做成分/不可以省。注意：引导主语从句，不能用if，只能用whether。例如：Whetherwewillholdapartyintheopenairtomorrowdependsontheweather.Whethersheiscomingornotdoesn’tmattertoomuch.（3）用连接代词引导的主语从句在由连接代词who,whose,whom,which,what,whoever,whomever,whichever,whatever引导的名词性从句中，其连接代词在句中起名词性作用，担当一定成分.例如：Whatyouneedismorepractice.WhatIwanttoknowisthis.Whateverwedoistoservethepeople.注：whatever/whoever的功用whatever,whoever在主语从句中不含疑问意义。它引导主语从句，并在从句中作主语、宾语、表语等。whatever=anythingthat;whoever=anyonewho。要注意和whatever,whoever引导的让步状语从句的区别。如：Whoeverbreaksthelawshouldbepunished.（主语从句）（＝Anyonewhobreaksthelawshouldbepunished.）Whoeverbreaksthelaw,heshouldbepunished.（让步状语从句）（＝Nomatterwhobreaksthelaw,heshouldbepunished.）（4）用连接副词when,where,why,how引导的名词性从句(其连接副词有含义,在句中作状语。)例如:Whereweshouldleaveitisaproblem.Whentheywillcomehasn’tbeenmadepubic.三.注意点:it构成的主语从句（1）由连词that引导的主语从句，在大多数情况下会放到句子的后面，而用代词it作形式主语。例如：Thatlighttravelsinstraightlinesisknowntoall.=Itisknowntoallthatlighttravelsinstraightlines.Whentheplaneistotakeoffhasnotbeenannounced.=Ithasnotbeenannouncedwhentheplaneistotakeoff.(但当what引导的主语从句表示“…的东西”时，一般不用it作形式主语。)错:Itisabookwhathewants.对:Whathewantsisabook.另外，需要注意的是，it作形式主语代替主语从句时，要注意和as引导的定语从句的区别。试比较：ItwasreportedthattheUSwasundertheterroristattack.Aswasreported,theUSwasundertheterroristattack.（2）常见用it作形式主语的复合句结构aItis+名词+从句Itisafactthat…事实是……Itisgoodnewsthat………是好消息Itisaquestionthat………是个问题Itiscommonknowledgethat………是常识类似的名词还有：apity；awonder；agoodthing；nowonder；surprise等。例如：Itisamysterytomehowitallhappened.Itiscommonknowledgethatthewhaleisnotafish.ItisnosurprisethatBobshouldhavewonthegame.It’sapitythatyoumissedthefilm.bItis+形容词+从句Itisnecessarythat…有必要……Itisclearthat…很清楚……Itislikelythat…很可能……Itisimportantthat…重要的是……类似的形容词还有：strange;natural;obvious;true;good;wonderful;possible;unlikely;quite;unusual;certain;evident;worth-while;surprising;interesting;astonishing,etc.例如：Itisdoubtfulwhethershewillbeabletocome.Itwasreallyastonishingthatherefusedtotalktoyou.Itisessentialthatheshouldbeherebytheweekend.Itseemsobviousthatwecannotgoonlikethis.Itisnecessarythatyou（should）masterthecomputer.ItisimportantthatastudentlearnEnglishwell.It’sclearthattheybadlyneedhelp.Itislikelythatahurricanewillarrivesoon.需要注意的是，这类主语从句中，谓语动词很多为“（should）＋动词原形”，即要用虚拟语气。cItis+过去分词+从句Itissaidthat…据说……Itisreportedthat…据报道……Ithasbeenprovedthat…已证明……Itmustbeprovedthat…必须指出……类似的过去分词还有：known;estimated;expected;believed;thought;hoped;noted;discussed;required;decided;suggested;demanded;madeclear;foundout,etc.例如：Itisthoughtthatheisthebestplayer.Itisestimatedthatthevaseis2000yearsold.Itisusedtobethoughtthatanewstarmustbeduetoacollisionbetweentwostars.Ithasnotbeenmadeclearwhenthenewroadistobeopenedtotraffic.Itissaidthathewaskilledintheearthquake.dItseems（happened/appears/doesn’tmatter/makesnodifference/occurred…）that…如：Itseemsthattheywillwinthegame.Itmakesnodifferencewhetherhewillattendthemeetingornot.ItdoesnotmatterifImissedmytrain.IthappenedthatIsawhimyesterday.四．练习1._____asmuchasone-fifthofalltimberharvestedisnotused.A.TheestimateB.TheestimatedC.TheyareestimatedD.Itisestimatedthat2._____somemammalscametoliveintheseaisnotknown.A.WhichB.SinceC.AlthoughD.How3._____wehaveachievedisattributedtotheguidanceofourparents.A.WhoeverB.WhateverC.HoweverD.That4._____wealthydoesnotnecessarilymeanthatamanisgreedy.A.ForthereasonthatheisB.JustbecauseheisC.ThereasonofbeingD.Thatheis5.Although___happenedinthisdevelopedcountrysoundslikesciencefiction,itcouldoccurelsewhereintheworld.A.whichB.whatC.howD.it6._____shehadforgottentotakehernotebook.A.ThatoccurredtoherB.SheoccurredthatC.ToherthatoccurredD.Itoccurredtoherthat7.Iamsurethat_____shesaidiswrong.A.whichB.allC.thisD.what8.Welostourwayintheforest,and____mademattersworsewasthatitwasgettingdark.A.thatB.whichC.itD.what9._____ornotisstilluncertain.A.He’scomingB.IfheiscomingC.ThatcomingD.Whetherhe’scoming10.It’s_____he’llbeabletocome.A.doubtwhetherB.doubtfulC.doubtitD.doubtfulwhether11.______heisatworkintheheartofthebigcityorathomeinthequietsuburb,Dick’slifeistiedtomachines.A.WhetherB.TillC.IfD.Unless12._____hesawbothsurprisedandfrightenedhim.A.ThatB.WhenC.WhatD.Which13._____iswarmsunshine.A.Whatdoweallneed.B.WhatallweneedC.WhatweneedD.Whatweallneed14._____isapitythatheshouldfeelsoupset.A.WhatB.ThatC.HeD.It15._____aspoonfulofsoilcantellussomuchaboutthestructureandearlyhistoryofthemoon.A.RemarkableB.QuiteremarkablyC.ItisremarkablethatD.Itisremarkablefactthat16._____younominatewillbeelected.A.WhoB.WhomC.WhomeverD.That’s17._____bookyouborrowmustbereturnedwithinaweek.A.WhatB.WhichC.WhicheverD.That’s18._____ofusgetshomefirststartscooking.A.WhoB.WhichC.WhicheverD.Anyone