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主语从句一、主语从句的连词分三类（1）从属连词引导的主语从句（thatwhetherif）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。That引导主语从句通常用it作形式主语。例如：Thatyouwillwinthemedalseemsunlikely.Thatshesurvivedtheaccidentisamiracle.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不能在开头，只能用whether。Whetherwewillholdapartyintheopenairtomorrowdependsontheweather.Whethersheiscomingornotdoesn’tmattertoomuch.（2）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.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.）（3）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、it作形式主语的主语从句有时为了考虑句子平衡，通常在主语从句处使用形式主语it，而将真正的主语从句移至句末。这分四种情况：(1)对于以连词that引导的主语从句，通常用形式主语it替代主语从句：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。Itisamysterytomehowitallhappened.Itiscommonknowledgethatthewhaleisnotafish.ItisnosurprisethatBobshouldhavewonthegame.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.Itisdoubtfulwhethershewillbeabletocome.Itisessentialthatheshouldbeherebytheweekend.Itseemsobviousthatwecannotgoonlikethis.Itisnecessarythatyou（should）masterthecomputer.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：Itisusedtobethoughtthatanewstarmustbeduetoacollisionbetweentwostars.Ithasnotbeenmadeclearwhenthenewroadistobeopenedtotraffic.dItseems不及物动词（happened/appears/doesn’t’tmatter/makesnodifference/occurred…）that…主语从句不可提前Itmakesnodifferencewhetherhewillattendthemeetingornot.ItdoesnotmatterifImissedmytrain.IthappenedthatIsawhimyesterday.(2)对于以连接代词(副词)引导的主语从句，可以使用形式主语代主语从句，也可直接在句首使用主语从句：Whethertheywouldsupportuswasaproblem.他们是否会支持我们还是一个问题。Itwasaproblemwhethertheywouldsupportus.他们是否会支持我们还是一个问题。(3)对关系代词型what引导的主语从句，通常直接将主语从句放在句首。如：Whatweneedismoney.我们需要的是钱。WhatIwanttoknowisthis.我想知道的就是这一点。有时也可将助用形式主语。如：Itisclearenoughwhathemeant.他是什么意思很清楚。(4)如果句子是疑问句，则必须用带形式主语it的结构：Isittruethatheisthegirl’sfather?他是那女孩的父亲，是真的吗？Howisitthatyouarelateagain?你怎么又迟到了？四、连词that的省略问题引导主语从句的连词that有时可省，有时不能省，其原则是：若that引导的主语从句直接位于句首，则that不能省略；若that引导的主语从句位于句末，而在句首使用了形式主语it，则that可以省略：Thatyoudidn’tgotothetalkwasapity.很遗憾你没去听报告。(that不可省)Itwasapity(that)youdidn’tgotothetalk.很遗憾你没去听报告。(that可省)高考题：1、Itneveroccurredtome__C_youcouldsucceedinpersuadinghimtochangehismind.(陕西高考)A．whichB．whatC．thatD．If首先要理解句意.这句话的意思是说,我从来没想到你能够成功地说服他去改变,而不是我从来没想到你能否成功地说服他改变.第二,Itneveroccurredtome是用于对于某个已发生的事实表示惊讶、吃惊的句型,所以这里youcouldsucceedinpersuadinghimtochange这个事实只能用that来引导；if是用于引导一个不确定性（uncertainty）的,这里不可以用.2、It'sobvioustothestudents___B_____theyshouldgetwellpreparedfortheirfuture.(天津卷)A．asB．thatC．whichD．Whether考查名词性从句中的主语从句用法.此处要分析句子结构,看出it为形式主语,代替thattheyshouldgetwellpreparedfortheirfuture,并且本句意思完整,故选D.3、____B____somepeopleregardasadrawbackisseenasaplugbymanyothers.(2010·北京)A．WhetherB．WhatC．ThatD．How考查名词性从句中的主语从句用法.此处要分析句子结构,看出it为形式主语,代替thattheyshouldgetwellpreparedfortheirfuture,并且本句意思完整,故选D.4、Itisuncertain____A____sideeffectthemedicinewillbringabout，althoughabouttwothousandpatientshavetakenit.(2010·浙江)A．thatB．howC．whatD．Whetherwhether是“是否”的意思这里应该是选B,what.因为跟后面sideeffect连起来,whatsideeffect,一起表示“是什么副作用”整句话的意思是“虽然有两千多个病人服用的这个药,但是对于其带来的具体的什么副作用还是不明确的.”根据意思来选择,只能是Bthat,how,whether都不能表达这个意思.主语从句练习题1.____C____makesmistakesmustcorrectthem.A.WhatB.ThatC.WhoeverD.Whatever这句话强调的是普遍性，所以用whoever——任何人，而不是特指谁2.Itworriedherabit___B_herhairwasturninggrey.A.whileB.thatC.ifD.for解析：句意：她的头发渐渐变得花白,使她不安.该题常错选C、D.用if和whether引导该句则句意不通.主语从句较长时,多放在句子后部,用it作形式主语,此时,that也不能省略.3.Whenandwhyhecamehere____A____yet.A.isnotknownB.arenotknownC.hasnotknownD.havenotknown因为,首先,这是现在完成时,yet是现在完成时的提示词,但是也可以是一般现在时第二,Whenandwhyhecamehere这个整个句子做主语,凡是句子做主语的,都是单数,因此是IS第三,这是被动,他何时来为什么来,还尚未为人所知悉如果是现在完成时,是hasnotbeenknown4.___C_____isnoreasonfordismissingher.A.BecauseshewasafewminuteslateB.OwingtoafewminuteslateC.ThefactthatshewasafewminuteslateD.Beingafewminuteslate首先,句子不完整,缺的是可以充当主语的名词性的从句.A和B排除,都不是D如果真的要选的话,应该为：Beingafewminuteslateisnoreasonforherbeingdismissed.这个叫主语一致吧C由thefact引导的同位语名词性从句符合要求,主干是：thefactisnoreasonfordismissingher.5.___D_____Tomlikedtoeatwasdifferentfrom________.A.That…thatyouhadexpectedB.What…thatyouhadexpectedC.That…whatyouhadexpectedD.What…whatyouhadexpected选A.A.wha