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It作形式主语常见句型动词不定式，动名词或主语从句作主语时，通常把它们放在谓语动词前，而用it作形式主语，放到句首，常见句型有：1.It+be+形容词+主语从句，如：ItisuncertainwhetherhecancometoJenny’sbirthdaypartyornot.2.It+be+名词词组+主语从句，这类名词有：afact,apity,ashame,anhonour，aquestion等，如：It’sapitythatyoumissedtheexcitingfootballmatch.Itremainsaquestionwhetherhewillcomeornot.3.It+be+过去分词+主语从句，这类过去分词有：announced,believed,expected,hoped,decided,reported,said,shown等，如：Itisreportedthat16peoplewerekilledintheearthquake.Itisnotdecidedwhowillgivetheoperationtothepatient.4.It+不及物动词(seem,appear,happen等)+主语从句,这类不及物动词有：appear,happen,seem等，如：Itseemedthathedidn’ttellthetruth.IthappenedthatIwasoutwhenhecalled.5.It+be+形容词+forsb.）+动词不定式这类句型常用形容词easy,difficult,hard,important,possible，wise等作表语，有时候为了强调不定式动作的执行者，常在不定式前加forsb，如：It’snecessaryfortheyoungtomastertwoforeignlanguage.Itisunwisetogivethechildrenwhatevertheywant.这类形容词有：easy,difficult,hard,important,possible，wise6.It+be+形容词+ofsb.+动词不定式，这类形容词常是表示心理品质,性格特征的形容词，如：kind,nicestupid,clever,foolish,polite,impolite,silly,selfish,considerate等。某人和这些形容词可以构成主系表结构。如：It’sverykindofyoutohelpmewiththework.=Youarekindtohelpme.Itseemedselfishofhimnottosharehisdictionarywithothers.=Heseemedselfishnottosharehisdictionarywithothers.7.It+be+名词词组+动词不定式，如：Itisnotagoodhabittostayuptoolate.8.It+be+名词或形容词+动名词，这类名词和形容词常常是：good,nogood,nouse,awasteof,useless,senseless等，如：It’sawasteoftimetalkingtoheranymore.Itisnousearguingaboutthematterwithhim.9.It+take(sb.)+时间（金钱）+动词不定式，如：Ittooktheworkersalmostthreeyearstofinishbuildingthedam.Itwilltakeawholedaytogettothetopofthemountainonfoot.实战演练：1.Itisgenerallyconsideredunwisetogiveachildheorshewants.(NMET1997)A.howeverB.whateverC.whicheverD.whenever2.Infactisahardjobforthepolicetokeeporderinanimportantfootballmatch.(2001上海)A.thisB.thatC.thereD.it3.isafactthatEnglishisbeingacceptedasaninternationallanguage.(NMET1995)A.ThereB.ThisC.ThatD.It4.Isnecessarytotakeoffourshoeswhenweenterthelab?(MET88)A.everyoneB.thisC.herD.it5.________willtakeyoualotoftimetofindhiminthecrowd.A.ItB.IC.WeD.They6.Itisnousehis_________there,thesituationishopelessnow.A.togoB.tobegoingC.goingD.havinggone7.Itisnevertoolatetolearn,________?A.isitB.isn’titC.doesitD.doesn’tit8.___________isknowntoallthatShenzhouVILaunchedSuccessfully.A.AsB.WhatC.ItD.That9._______isreportedinthenewspaper,theEarthquakeineastChina'sJiangxiProvincekilled13peopleA.ItB.AsC.ThatD.What10.___________certainthathisinventionwillmakepeople’slifeconvenient.A.That’sB.ThisisC.It’sD.What’s11._________thatthereisanotherfootballmatchontheairthisevening.A.ItsaysB.ItwassaidC.ItissaidD.Whatwassaid12.__________thattheirdaughtergotanopportunitytostudyabroad.A.It’saexcitingnewsB.ThisisanexcitingnewsC.ThisisexitingnewsD.It’sexcitingnews参考答案：1——5BDDDA6——10CACAC11——12CD㈠it作形式主语：it作形式主语时没有具体的意义，而只是帮助把真正的主语移到句子后部去，使句子显得平稳一些。it作形式主语时，可以代替三种形式：不定式、动名词和主语从句。⒈it代替不定式短语常用于下列句型中：It+be+形容词+(for/ofsb.)todosth.It+be+名词+todosth.Ittakessb.sometimetodosth.干…花了某人…时间It’suptosb.todosth.干…是某人的职责或义务①Itiseveryone’sdutytoobeythelaw.遵守法律是每个人的义务。（it作形式主语,代替不定式短语toobeythelaw）②ItisdifficultforaforeignertolearnChinese.对于一个外国人来说，学习汉语是困难的。（it作形式主语,代替不定式短语tolearnChinese）③Itisnotrighttousetheseplacesasrubbishdumps.把这些地方用来倒垃圾是不对的。（it作形式主语,代替不定式短语tousetheseplacesasrubbishdumps）④Ittookthemayeartobuildthebridge.建这座桥花了他们一年的时间。（it作形式主语,代替不定式短语tobuildthebridge）◆Itbe+形容词+forsb.todosth.与Itbe+形容词+ofsb.todosth.：如果句型中的形容词描述的是sb.的品质、品格，在逻辑上可以作sb.的表语，则sb.前应用介词of，否则就用for。①It’snecessaryforustouseashort-waveradiotopickuptheprogrammes.我们用一台短波收音机收听这些节目是必要的。③It’skindofyoutohelpme.感谢你对我的帮助。（=Youarekindtohelpme.）④Itwasfoolishofhimtogiveupthejob.他放弃那工作是愚蠢的。（=Hewasfoolishtogiveupthejob⒉it代替动名词短语：动名词作主语用后置形式的情况远不及不定式那么普遍，常限于nogood,nouse,useless,waste等词的后面。①Itisnogood/usehavingacarifyoucan’tdrive.如果你不会开车，有车也没用。(it作形式主语,代替动名词短语havingacar)②ItisawasteoftimewatchingTV.看电视是浪费时间。（it作形式主语,代替动名词短语watchingTV）③Itisnouseaskinghim.问他没有用。（it作形式主语,代替动名词短语askinghim）⒊it代替主语从句：这个主语从句可以用连词that引导，也可以用连接代词或连接副词引导。①Itwasclearthattheyhadnodesireforpeace.很清楚他们没有和平的诚意。（it作形式主语,代替主语从句thattheyhadnodesireforpeace）②Itisdoubtfulwhethershewillbeabletocome.她能否来还很难说。（it作形式主语,代替主语从句whethershewillbeabletocome）③Itwasclearenoughwhatshemeant.她的意思是够清楚的。（it作形式主语,代替主语从句whatshemeant）用it作形式主语，把真正的主语从句移至后面的常见句型有：◆Itisapity/ashame/afact/anhonour/goodnews/nowonder/awonder…that…①Itwasapitythattheengineercouldn’tcome.可惜工程师没能够来。②Itisawonderthathecontinuestogamblewhenhealwaysloses!令人惊讶的是他一直输还一直赌。◆Itis+形容词（如：strange/natural/surprising/obvious/true/fortunate/wonderful/funny/possible/impossible/likely/unlikely/clear/unusual/certain/important…）that…①Itiscertainthathewillwin.他一定会取胜。。◆Itseems/happened/turnedout/suddenlystruckme/occurredtome…that…①IthappenedthatIwasn’ttherethatday.恰好那天我不在那里。◆It+be+过去分词（如：said/reported/announced/decided/expected/hoped/known/believed…）that…②Itissaidthatnothinghasbeendoneaboutit.据说至今对此没采取任何措施。③Itisreportedthatmorethantwentypeoplewerekilledinthatbusaccident.据报道在那次的公共汽车事故中有二十多人丧生。*注意要在Itissuggested/required/desired/ordered/proposed…that…的主语从句中用虚拟语气：(should)+动词原形①Itisrequestedthathegiveaperformanceatthepart