It的用法指代已提及的事物Eg:--Whoseisthisdictionary?--Itismine.指代天气、时间、距离、地点、自然现象、环境等。Eg:--Whattimeisit?--It’sseven.作形式主语。代替todo,doing或主语从句。Itbethat+adj+主语从句Eg:Itispossiblethatweallarrivetheretomorrow.Itbe+名词/名词词组+主语从句常用的名词：afact/apity/ashame/nowonder/commonsense(常识）Eg:It’sapitythatwelostthegame.Itiscommonsensethatdrinkingmuchwaterafteramealisharmfultoyourhealth.Itbe+过去分词+主语从句常用的过去分词：said/reported/announced/knownItbe+adj+todoItbe+名词/名词词组+todoEg:Itisagoodhabittogetupearly.Ittakessb+时间+todosthItisuptosbtodosthItis+名词/名词词组/形容词+doingsth常用的词：nouse/nogood/useless/senselessit作形式宾语，代替后面作真实宾语的不定式（todo,doing形式或宾语从句）Eg:IthinkitdifficulttolearnEnglishwell.Ithinkituseless/nousesayingtoomuch.Ithinkitnecessarythatwemastersomefirstaidskills.用于某些惯用语中Makeit(成功，做成）Believeitornot(信不信由你）Igotit（我明白了）Keepatit(别松劲）Icannothelpit(我无能为力）强调句（itwas/is+被强调的部分+that/who+句子的其他的成分）被强调的部分为：主语，状语（时间状语、地点状语、原因状语、方式状语），宾语。Eg:Hemetastrangewomanattherailwaystationyesterday.强调主语：Itwashethat/whometastrangewomanattherailwaystationyesterday.强调宾语：Itwasastrangewomanthat/who/whomshemetintherailwaystationyesterday.强调状语：Itwasattherailwaystationthathemetastrangewomanyesterday.强调句的一般疑问句：Is/was+it+被强调的部分+that+其他成分？强调句的特殊疑问句：特殊疑问词+is/was+it+被强调的部分+that+其他成分？Eg:whowasitthatmetastrangewomanattherailwaystationyesterday.强调句型的否定转移Itis/wasnotuntil......thateg:Itwasnotuntilsixo’clockthatthetrainsetoff.