it作形式主语为避免主语冗长,句子头重脚轻,经常用it作形式主语,主语从句放在后面作真正的主语。1.Itiscertainthathewillsucceed.2.Itisnotknownwhetherhewillgothere.3.Ithasnotbeendecidedyetwhenthey’llstarttheproject.“It”isusedasemptysubject.形式主语1.Itis＋名词＋从句Itisafactthat…事实是…Itisanhonorthat…非常荣幸Itiscommonknowledgethat…是常识能获邀参加你们的婚礼真是不胜荣幸风就是流动的空气,这是常识可惜他由于一个拼写错误没有得满分It’sagreathonorthatIhavebeeninvitedtoyourwedding.It’scommonknowledgethatwindismoving/flowingair.It’sapitythathedidn’tgetfullmarksbecauseofaspellingmistake.句型1.2.Itis+adj.+从句It’scertainthat…肯定…Itispossiblethat...很可能……Itisunlikelythat...不可能……Itisobviousthat…很明显…Itisnecessary\important\natural\...that…*_________________(很可能)shewillcomebacktomorrow.*_________________(很明显)thismeasureiseffective.+(should)+do…ItispossiblethatItisobviousthat句型2.另注意在主语从句中用来表示惊奇、不相信、惋惜、理应如此等语气时，谓语动词要用虚拟语气“(should)+do”，常用的句型有：Itisnecessary(important,natural,strange,etc.)that…Itissuggested(requested,proposed,desired,etc.)that…3.Ithappens(seems,looks,appears)that...该句型中it是形式主语，that引导的是主语从句,主句中的happen,seem等词是不及物动词．Ithappened(sohappened)thathemethisteacherinthestreet.碰巧Itseemsthathewillbebackinafewdays.句型3.Itseemsthatsb.do/bedoing/havedone/haddone=Sb.seemstodo/bedoing/havedone/tobedone/tohavebeenItseemedthathehadbeentoBeijingbefore.=HeseemedtohavebeentoBeijingbefore.It+不及物动词+从句Ithappenedthat...碰巧……Itoccurredtomethat…我突然想起…*________________(刚好)Icameintotheofficeatthattime.*____________________(我突然想起)Iforgettosenttheletter.IthappenedthatItoccurredtomethat句型4.据说他读过这篇小说.Itwassaidthathehadreadthisnovel.=Hewassaidtohavereadthisnovel.It+be+-ed分词+that-从句Itissaidthat……据说……Itisknownthat……据了解……Itisreportedthat……据报道……Itisbelievedthat……据认为……1.据说她两年前在美国留学2.It’ssaidthathestudiedinAmericatwoyearsago3.2.据说她现在正在美国留学4.It’ssaidthatheisnowstudyinginAmerica5.3.据说她现在懂三国外语6.It’ssaidthatheknowsthreeforeignlanguagesHeissaidtohavestudiedinAmericatwoyearsago.HeissaidtobestudyinginAmericanow.Heissaidtoknowthreeforeignlanguages.Itissuggested(ordered,required...)that...该句型和上一个同属一个句型。主句中的过去分词是表示请求，建议，命令等词时，that后的从句要用虚拟语气（should+动词原形），should可以省。常译为“据建议；有命令……）”。Itissuggestedthatthemeeting(should)beputoff.Itwasorderedthatwe(should)arrivethereintwohours.注意Itisdoubtfulwhethershewillbeabletocome她是否能来还不还说。Itwasclearenoughwhatshemeant.她的意思还不太清楚。Itwon’tmaketoomuchdifferencewhetherhewilljoinus.他是否参加我们队不会太重要。Hasitbeenfoundoutwhosettherecord?是谁破了纪录弄清楚了吗？5、可用whether和疑问词引导从句的有：Itisdoubtful(notknown,notdecided,notmadeclear,tobefoundout,beingconsidered,amystery,aquestion,+that/whether句型5Itisstillaquestionwhenweshallhaveoursportsmeeting.Itisamysterytomehowitallhappened.这事是怎么发生的还是个谜。Ithasn’tmadeclearwhenthenewroadistobeopenedtotraffic.新路什么时候通车还不清楚。6.6.Itdoesn’tmatterhow/whether(if)(if)…结构中的主语从句不可提前。该句型中whether(if)引导的从句是真正主语，该句型常译为“不论（是否）……没关系……。Itdoesn'tmatteriftheyareold.Itdoesn’tmatterwhowi...
