典型的主语从句Whatyouneed作为整个句子的主语例如:whowillgowithushasn'tyetbeendecided.此句whowillgowithus作为整个句子的主语主语从句(SubjectClause)定义:如果一个句子在复合句中充当一个主语,那么这个句子就是主语从句.第一部分：常规主语从句,即句子在复合句中充当一个主语（1）Thathefinishedwritingthecompositioninsuchashorttimesurprisedusall.（2）Whetherwewillgoforanoutingtomorrowremainsunknown.（3）Whowillbeourmonitorhas'tbeendecidedyet.（4）Whomwemuststudyforisaquestionofgreatimportance.（5）Whatcausedtheaccidentremainsunknown.（6）Whateveryoudidisright.（7）Whosewatchwaslostisunknown.（8）Whatweneedistime.（9）Whatweneedaregooddoctors.小结:（1)引导主语从句连词有that,whether,who,what,whatever等（2)连词位于句首不能省略（3)主语从句大多数情况下视为单三,但也有例外,如例9第二部分：为了防止句子头重脚轻,通常把形式主语it放在主语位置,真正主语搁置于句末（1）Itiscertainthathewillwinthematch.（2）Itistruethathehasmadeaveryimportantdiscoveryinchemistry.（3）Itisverylikelythattheywillholdameeting.（4）Itisstrangethatheshoulddothat.（5）Itisimportantthatweallshouldattendthemeeting.（6）Itisstrangethatthemanshouldhavestucktohissillyideas.（7）Itisapitythatwewon'tbeabletogotothesouthtospendoursummervacation.（8）Itisstillamysterywhatcausedtheaccident.（9）Itissaidthathehasgonetoshanghai.(=Heissaidtohavegonetoshanghai)（10）ItisknowntoallthatthegunpowderwasfirstinventedbytheChinese.（11）Itissuggestedthattheworkshouldbedonewithgreatcare.（12）Itseemsthathehasseenthefilm.(=Heseemstohaveseenthefilm)（13）Ithappenedthatthetwocheatswerethere.(=Thetwocheatshappenedtobethere)小结:（1)以that引出的主语从句,常以形式主语it引导.Itis+形容词/名词/某些动词ed+that从句.（2)在有些that从句中要用虚拟语气(should+do/should+havedone)例句4,5,6,11.