主语从句详解.doc
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主语从句详解
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.
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,在多数情况下放到句子的后面,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
A.Itis+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.
B.Itis+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.
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.
C.Itis+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.
D.Itseems（happened/appears/doesn’tmatter/makesnodifference/occurred…）that…
Itseemsthattheywillwinthegame.
Itmakesnodifferencewhetherhewillattendthemeetingornot.
ItdoesnotmatterifImissedmytrain.
IthappenedthatIsawhimyesterday.
主从练习
1._____ as much as one-fifth of all timber harvested is not used.
A. The estimate B. The estimated
C. They are estimated D. It is estimated that
2. _____ some mammalscame to live in the sea is not known.
A. Which B. Since C. Although D. How
3. _____ we have achieved is attributed to the guidance of our parents.
A. Whoever B. Whatever C. However D. That
4. _____ wealthy does not necessarily mean that a man is greedy.
A. For the reason that he is B. Just because he is
C. The reason of being D. That he is
5. Although ___ happened in this developed country sounds like science fiction, it could occurelsewhere in the world.
A. which B. what C. how D. it
6. _____ she had forgotten to take her notebook.
A. That occurred to her B. She occurred that
C. To her that occurred D. It occurred to her that
7. I am sure that _____ she said is wrong.
A. which B. all C. this D. what
8. We lost our way
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