1．代替上文中提到過的人或事物。指代人時(shí)，一般用于小孩或不十分的人－Whoisthe－It‘smyteacher’s－Whoisthat－It'smyfriendTom．He(It)wantstoseeyou．It’shalfanhour’swalkfromheretoourIt‘sniceandwarmButit'stwoo'clocknow,andit'stimeforustogoto用作形式主語.it沒有具體意義，而只是幫助把真正的主語移至句子后尾，使句子顯得平it給移至句子后尾的主語有三種：一種由不定式表示，一種由動名詞表示，1).It替代真正的主語——動詞不定式短語.Itiseasiertosaythantodo.Itisagoodacttohelpthe2).it替代真正的主語——動名詞短語,nogoodnouse,noharm,dangerous,foolish等詞作表語的句中.It’snoharmdrinkingrunningwaterinthatarea。It’sfoolishtalkinglikethat.3).itit的句子很多,①Itisapity(ashame,afact,awonder,agoodthing,etc.)that…Itisashamethathedidn’tpasstheexam.Itisstrangesurprising,obvious,truegood,possible,clearetcthat…Itwasclearthattheyhadnodesirefor③Itseems(happened,turnedout,Itseemedthatthingswerenotasthey④Itissaid(decided,expected,etc)that…Itissaidthattheticketshavebeensoldout.當(dāng)復(fù)合賓語中的賓語是不定式,－ingit作形式賓語,而將真正的賓語WefinditdifficulttolearnEnglishwellinsuchashortWethinkitnousecryingoverspiltWemadeitclearwhenandwhereweweregoingtohavethemeeting．5．用于強(qiáng)調(diào)句型，即“Itis/was＋被強(qiáng)調(diào)部分＋that/who/whom+其它”句型之中。①強(qiáng)調(diào)句的謂語is或was用單數(shù)ItwasyesterdaythatImetyourfatherinthethatwhere、when等連詞ItwasinthestreetthatImetyourfatherwho(主格或賓格)whom(賓格)thatthatItwasyourfatherthat/whom/whoImetinthestreetItwasIthat/whometyourfatherinthestreetItistheywhoareourItwasnotuntilteno'clockthatwegothomelastItwasteno'clockwhenwegothomelastnightItwasatteno'clockthatwegothomelastnightwhen不可改為that,因?yàn)槿サ鬷twas和that“Wegothometeno'clocklastnight．”這樣一個(gè)不完整的句子；第二句是強(qiáng)調(diào)句，thatwhen．Itisclear(obvious，true，possible，certain…)Itisimportantthat后的從句應(yīng)用虛擬語氣動詞)，should可以省去Itisnogood ngItisapity(ashame…)本句型中，that后的從句一般用虛擬語氣(should十動詞)，should可以省去。表Itistime(abouttime，hightime)thatItisthefirst(second…)timeItissaidItissuggested(ordered…)本句型中的過去分詞應(yīng)該是表示請求、建議、命令等的詞，that后的從句要用虛擬語氣(should十動詞)，should可以省略。常譯為“據(jù)建議；有命令……”。Ithappens(seems，appears)Ittakessb…todoItdoesn’tmatterItiskind(ofsb)todo本句型中的不定式如果需要邏輯主語，則須要前置介詞of，而句型中的形容詞必須是horrible，kind，lazy，modest，naughty,polite，rude，silly,stupid，wise，wrong等。Itisnecessary(forsb)todoItis(just)likesbtodo本句型為“(恰恰)是……樣子”。用來表示贊揚(yáng)或不滿，若用否定式，則表示懷疑。例：It'slikehimtoleavetheworktoothers．Itisuptosbtodo本句型表示“誼由做……”Itis+被強(qiáng)調(diào)部分It本句型主句中用時(shí)間作表語，一般用現(xiàn)在時(shí)或完成時(shí)，since引導(dǎo)的從句常用瞬間動詞ItItlooks(seems)asasif“看起來好像……”例 Itlooksasifheisill(真的病了)例 Itlooksasifhewere (沒有生病)it iswellknowtousallthattheearthis iswellknowntousall,theearthisA. B. C. D.①②I

doesn’tmattermuchwhetherhe’llcometotheparty.anhonortobeinvitedtospeakhere.A. B. C. D. nowonderthathehaspassedthe noneedforyoutowaitA.There B.It C.It D.There①Wasitthehouse AbrahamLincolnwas②Wasitinthehouse AbrahamLincolnwasA. B. C. D.bothAand①It’sverykind youtohelp②It’sveryimportant youtokeepthebalanceofA. B. C. D. ①Itisnogood sucha②It’sofnoimportance suchaA. B.to C. D.①It'stimethatwe to②Itisthesecondtimethatwe toA. B. C.have D.have①It