英语语法专题讲座名词从句名词从句的概念?在句子中起名词作用的句子叫名词从句（NounClauses）。名词从句的功能相当于名词词组，具有名词的语法功能，可分为主语从句、宾语从句、表语从句和同位语从句。名词从句?引导名词从句的连接词可分为三类：连接词that，whether，if（不做句子成分，只起连接作用）；连接代词what，whatever，who，whoever，whom，whose，which，whichever；连接副词when，whenever，where，wherever，how，however，why等。引导主语从句的连接词?引导主语从句的词有：?连接词：that,whether,if(只限it作形式主语时用)?疑问代词:who,what,which?疑问副词：when,where,how,why在主语从句中应注意的问题?1.主语从句一般用it作形式主语，放在句首，而将主语从句放到句末。如：?Itispossiblethathehasstolenthecar.很可能他偷了小车。?Isn’titstrangethatheshouldnothavepassedthetest?他测试没有通过，难道不奇怪吗？?2.if引导主语从句时，只能用it作形式主语，放在句首，而将if引导的主语从句放到句末。如：?ItisuncertainifhewillleaveforBeijingtomorrow.明天他是否去北京还不敢肯定。?3.that引导主语从句放在句首时，that不可省。如：?Thathewasillyesterdayisknownnow.大家都已知道他昨天生了病。?4.主语从句中主句的谓语动词一般用第三人称单数形式，但what引导主语从句的主句谓语动词的形式须根据句子的意思来判断。?Howheworkeditoutisstillasecret.他是如何把它做出来的还是一个秘密?WhattheymakeinthisfactoryareTVsets.他们在工厂里所做的东西就是电视机。用it作形式主语的结构?????????????(1)Itis＋名词＋从句Itisafactthat…事实是…Itisanhonorthat…非常荣幸Itiscommonknowledgethat…是常识(2)itis＋形容词＋从句Itisnaturalthat…很自然…Itisstrangethat…奇怪的是…(3)it不及物动词＋从句Itseemsthat…似乎…Ithappenedthat…碰巧…(4)itis＋过去分词＋从句Itisreportedthat…据报道…Ithasbeenprovedthat…已证实…it作形式主语的例句?（1）Itiscertainthathewillwinthematch.?（2）Itistruethathehasmadeaveryimportantdiscoveryinchemistry。?（3）Itisapitythatwewon'tbeabletogotothesouthtospendoursummervacation.?（4）Itisstillamysterywhatcausedtheaccident.?（5）ItisknowntoallthatthegunpowderwasfirstinventedbytheChinese.?（6）Itissuggestedthattheworkshouldbedonewithgreatcare.?（7）Itseemsthathehasseenthefilm.(=Heseemstohaveseenthefilm)?（8）Ithappenedthatthetwocheatswerethere.(=Thetwocheatshappenedtobethere)主语从句不可位于句首的五种情况?(1)if引导的主语从句不可居于复合句句首。?Whether（?≠?if）weshallhaveamatchremainsuncertain.?我们是否举行比赛还没有定下来。?It’snotimportantif（=?whether）youwinorlose.Whatisimportantishowyouplaythegame.?输赢并不重要，重要的是你如何打好比赛。?(2)Itissaid,(reported)…结构中的主语从句不可提前。例如：?ItissaidthatPresidentJingowillvisitourschoolnextweek.?(3)Ithappens…,Itoccurs…结构中的主语从句不可提前。例如：?Itoccurredtohimthathefailedintheexaminati