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英语·选修8(人教版)第四学时Grammar语法精讲名词性从句名词性从句包括主语从句、宾语从句、表语从句和同位语从句，在句中充当主语、宾语、表语、同位语，且用于陈述句句式。一、引导名词性从句的引导词可分为三类语法精讲1．连接词。(1)引导词that本身无词义，引导陈述句语气在从句中不充当成分。That_he_passed_the_examinationmadehismotherveryhappy.(2)引导词whether/if/asif有词义，但在从句中不充当成分，如whether，if和asif。Itseemsas_if_he_were_not_interested_in_this_project．语法精讲2．连接代词。引导词本身有词义且在句中充当成分，如who，whom，whose，what，which。Idon'tknowwho/whom_I_should_believe．3．连接副词。引导词本身有词义且在句中充当成分，如when，where，why，how。Wehaven'tdecidedwhen_we'll_go_to_Tibet．二、主语从句、表语从句和宾语从句语法精讲1.主语从句在整个句子中作主语，包含两类，形式主语和真正主语。(1)that引导主语从句时不能省略。That_the_driver_could_not_control_his_carwasobvious.(真正主语)Itwasobviousthat_the_driver_could_not_control_his_car．(形式主语)语法精讲(2)if不能用在句首引导主语从句，这时用whether；与ornot搭配表“是否”时，也只能用whether。Whether_he_left_(or_not)isunknown.(3)当主语是一个从句时，谓语动词一般用第三人称单数。What_we_needismoretimeandmoney.语法精讲2．表语从句出现在系动词后。Thetroubleisthat_we_are_short_of_money．Goandgetyourcoat.It'swhere_you_left_it．(1)引导表语从句除了上述三类词外还有because，asif/asthough等。请注意下列句型：①Thereason(why/forwhich...)isthat...Thereasonwhyhewasabsentwasthathewasill.Thereasonwhyhefailedintheexamisthathewassolazyandcareless.语法精讲②It/This/Thatisbecause...Itisbecause_you_don't_know_how_much_I_love_you．(2)连系动词appear，look，seem的两个常用句型：①Itseems/appearsthat...②Itlooks/seemsasif/asthough...(与事实相符用陈述语气，与事实相反用虚拟语气)Itseemsas_though_he_knew_nothing_about_the_truth．(3)as也可以引导表语从句。Thingsarenotalwaysas_they_seem_to_be．语法精讲3．宾语从句作及物动词、be＋形容词和介词的宾语。(1)宾语从句的时态与主句相呼应，但宾语从句表示的是客观真理或普遍现象时，从句谓语常用一般现在时。Theteachertoldusthat_the_earth_moves_around_the_sun．I'mafraidthat_it_will_rain_tomorrow．(宾语从句)Heisinterestedin_what_his_teacher_said．(介词＋宾语从句)语法精讲Theydoubtwhetherit_is_useful．(及物动词＋宾语从句)(2)连词whether和if可以互换，但要注意下列情况：①连词后紧跟ornot时用whether。Iwanttoknowwhether_or_not_they_will_come．②从句作介词宾语时用whether引导。Hewasinterestedinwhether_he_saw_her_there．③连接词后直接加不定式，不能用if只能用whether。Hedoesn'tknowwhether_to_stay_or_not．语法精讲④位于句首疑问语气的主语从句引导词，只能用whether.Whetherhewillsucceeddependsonhisattitude.⑤位于句首疑问语气的主语从句引导词，只能用whether.Whetherhewillsucceeddependsonhisattitude.⑤如果宾语从句是否定时，一般用if引导。Icareif_he_will_not_attend_the_meeting．(3)当宾语从句后带宾补时，要用句型“主语＋谓语＋it＋宾补＋that从句”。语法精讲Ithinkitcertainthat_she_will_do_well_in_her_exam．(4)当主语是I，we，动词think，believe，suppose，expect，imagine后带否定意义的宾语从句时，要将否定转移到主句。Idon't_thinkhewillwinthegame，willhe?语法精讲4．注意区分it作形式主语的主语从句与强调句的区别。强调句句型“Itis/was＋被强调部分＋that”，去掉“Itis/was...that”，句子仍然成立。Itisnaturalthat_they_should_have_different_views．(主语从句)It_isonlylatelythathehashadafamilyhimself.(强调句)It_wasinthehotelwherehestayedthatwediscussedtheseriousproblem.(强调句)语法精讲5．注意it作形式主语的主语从句和as引导的非限制性定语从句的不同。Itisknowntoallthat_the_earth_is_round．(主语从句)As_is_known_to_all，theearthisround.(非限制性定语从句)