课件15 主语从句
————课件15 一．定义
二．连接词分类及用法
三．It作形式主语
四．主语从句中谓语动词的数
五．主语从句中的虚拟语气
【习题精炼】
l．_ the 2008 Olympic Games will be held in Beijing makes the nation very excited．A．Whenever B．If C．Whether D．That
2．he said at the meeting astonished everybody present．
A．What B．That C．The fact D．The matter
3．It worried her a bit her hair was turning grey．
A．while B．that C．if D．for
4．leaves the room last ought to turn off the 1ights．
A．Anyone B．The person C．Whoever D．Who
5．they are most interested in is they can produce more and better cars．A．That；how B．What；how C．What；that D．That；that
6．I have will be yours sooner or later．
A．No matter what B．No matter how C．Whatever D．However
7．Word came I was wanted at the office．
A．which B．why C．that D．whether
8．we can’t get seems better th an we have．
A．What；what B．What：that C．That；that D．That：what
9．—has made our city Dalian she is today?
—It is the Party’s policy that has made it take on a new look．
A．What；that B．That；what C．there；so D．That；that
10．surprised me most was they had finished the work so quickly．
A．What：what B．That；that C．What：that D．That；what
11.________ the old man’s sons wanted to know was ________ the gold had been hidden.
A．That; what B．What; where C．What; that D．What; if
12.________surprised us very much that Tom should have left without a word.A．he B．It C．This D．That
13. _______ the sports meet will be held depends on the weather.
A. When ever
B. If
C. Whether
D. That
14. They lost their way in the forest and _____ made matters worse was that night began to fall.
A. that
B. this
C. what
D. which
15. _______ all the inventions have in common is _____they have succeeded.
A. What; what
B. That; that
C. What; that D That; what
15. ____ surprised me most was ______ they had finished it so quickly.
A. What, what
B. That, that
C. What, that
D. That, what
17. In some countries, ____ is called "equality" does not really mean equal rights for all people.
A. which
B. that
C. what
D. one
18. _____ they won the game was ______ we had expected.
A. That; which
B. Whether; that
C. What; that
D. That; what
19. ____ we can't get seems better than _____ we have.
A. What; what
B. What; that
C. That; that
D. That; what
20.___ surprised me most was ____ he was too late for the important meeting, for he was chairman of it.
A. What; why
B. That; how
C. What; how
D. That; why
21. _______ beat Xiao Wang black and blue is not known. A. Whom B. Whoever C. Who D. What
22. ___ the boy didn’t take the medicine made his mother very angry.A. That B. What C. How D. Which
23. ______ is unfit for the office.
A. It seems to me that
B. It seems to me that he
C. That seems he
D. That seems to him that
24. ____ is not known yet.
A. When she has gone
B. Where she has gone
C. How did she leave
D. Why did she go
Keys:1-5 DABCB 6-10 CCACC 11-12 BBCCC 16-20 CCDAA 21-24 ACABB
主语从句做主语，主句谓语动词的单复数需根据从句表示的单复数意义决定。1．what引导的主语从句做主语 （1）通常情况下，由what引导的主语从句放在句首时，其后的谓语动词，按语法一致的原则用单数。eg:What she said is correct. What caused the accident is not clear. （2）当主句中的表语是复数形式，或what从句的谓语动词及其补足语均为复数形式时，主句的谓语动词应用复数。eg:What he gave me are five English books. What are used as chief building materials today are steel and concrete. （3）当what引导的主语从句是一个由and连接的并列结构时，应根据句意确定其表达的单复数意义，然后决定主句谓语动词的单复数形式。 eg:What he says and acts does not concern me. What he says and acts do not agree. What I say and what I think are no business of yours. 2．由其它词引导的从句做主语时，谓语动词用单数形式。 Whether they will hold a party or not has not been decided. Who is responsible for the accidents is not clear. 3．当同一个主语从句是由两个不同的引导词引导时，因为它表达的还是同一件事，因此，谓语动词一般用单数。 eg:When and where we should hold the meeting has not been decided yet. 4．当主语是由两个由and连接的主语从句组成，通常表示的是两件不同的事情，主句谓语动词需用复数形式。 What you eat and how much you exercise are important factors in a weight loss program. What caused the accident and who was responsible for it remain a mystery to us.
名词性从句---主语从句 1. What is needed for the space trip is careful preparation. 2. Her wish is that she can lose weight soon. 3. I think that woman can reach every high achievements in many fields of science. 4. We were very excited at the news that our team had won. 引导名词性从句的关联词可分为三类： 一．从属连词：that（无任何词意） whether, if（均表示“是否”表明从句内容的不确定性） as if ,as though（均表示“好像”，“似乎”）以上在从句中均不充当任何成分二．连接代词：what, who, whom, which，whose, whatever, whoever, whichever(作主宾表定) 三．连接副词：when, where, how, why(作状语) I.主语从句 1.定义：在句子中担当主语的是一个从句,这个从句就叫做主语从句。 2.位置：主语从句是在复合句中充当主语的从句，通常放在主句谓语动词之前或由形式主语it 代替，而本身放在句子末尾。 3.引导主语从句的关联词： (1)从属连词that,whether,if (在从句中不充当成分，仅起连接作用) That Jack won the match yesterday surprised us. Whether he’ll come here isn’t clear. (此处不能用if) (2)连接代词who, whom, whose, what, which, whoever, whatever, whichever(充当主宾表定) What she did is not known. Whoever comes is welcome. (3)连接副词where,when,how,why(在从句中充当状语) How this happened is not clear to anyone. When the meeting will be held is decided by our manager. 4.有时为了避免头重脚轻，常用it作形式主语，而把真正主语放在句子末尾。 How the book will sell depends on its author. = It depends on its author how the book will sell. That he is the best student in the class is obvious. = It is obvious that he is the best student in the class. 用it作形式主语的几种常见结构： (1) It is ＋名词＋从句 It is a fact that … 事实是… It is an honor that …非常荣幸 It is common knowledge that …是常识 (2) It is ＋形容词＋从句 It is natural that… 很自然It is strange that… 奇怪的是… (3) It is ＋不及物动词＋从句 It seems that… 似乎… It happened that… 碰巧… It ap pears that… 似乎… (4) It ＋过去分词＋从句
主语从句造句： 1.How well the prediction will be validated by later performance depends upon the amount and reliability of the information used. 这些预测以后将在多大程度上被之后的表现证实，取决于所采用信息的数量和可靠性。 2.It is often important that you make it clear what your particular role is at a given time. 你要搞清楚在指定时期内你的特定角色是什么，这很重要。 3.It is reported that the unemployment rate is very high in many developed countries because financial crisis. 据报道，由于金融危机，很多发达国家的失业率都很高。 4.That mental health is important to physical condition is a fact. 精神健康对身体状况很重要，这是一个事实。 5.That he finished writing the composition in such a short time surprised us all. 他在这么短的时间内完成了写作使我们所有人都惊讶。 6.Whether we will go for an outing tomorrow remains unknown. 我们明天是否会去远足有待商榷。 7.What make the river more beautiful are the plants growing in the water. 为河水增色的是水里的荷花。 8.What struck me was that they have all suffered a lot. 给我印象深刻的是他们都受过很多苦。 9.Whether we will hold a party in the open air tomorrow depends on the weather. 我们明天是否在户外开晚会要看天气而定。 10.Which car you will choose to buy makes no difference. 你决定买哪一辆车都不会有任何区别。 11.It is common knowledge that honesty is the best policy. 诚实是最好的政策是共识。 12.What they need most is not financial aid or loan but advanced technologies and talents in certain key areas.
名词性从句之主语从句 一、名词性从句概述：在句子中起名词作用的各种从句统称为名词性从句。 根据它们在句中的语法作用，这类从句又可分为主语从句、同位语从句、表语从句和宾语从句。 二、主语从句定义： 在句中起主语作用的从句称为主语从句。 引导主语从句的连接词主要有：单纯连词（that, whether/ if）、连接代词(what, whatever, who, whoever, whom, whose, which, whichever等)和连接副词(when, where, why, how, whenever, wherever, however等)。 1)that引导的主语从句 （1）由连词that引导的主语从句:引导词that无含义/在句中不做成分/不可以省。例如：That you will win the medal seems unlikely.你能得奖看起来不大可能。 That light travels in straight lines is known to all. 众所周知，光沿直线传播。 That you don’t like him is none of my business.你不喜欢他不管我的事。（2）形式主语it替代主语从句位于句首，that引导真正的主语从句会放到句子的后面。常用的句式主要有如下几种： 1.It+ 系动词+形容词+that从句。 如： It is necessary that …有必要…… It is clear that …很清楚…… It is likely that …很可能…… It is important that …重要的是…… 类似的形容词还有：strange; natural; obvious; true; good; wonderful; possible; unlikely; quite; unusual; certain; evident; worth-while; surprising; interesting; astonishing, etc. 例如：It was really astonishing that he refused to talk to you. It is essential that he should be here by the weekend. It seems obvious that we can not go on like this. It is necessary that you （should）master the computer.
主语从句用法小结 勉县第二中学高二（7）班郭恬 指导老师：李艳 请观察下列句子, 注意主语从句的特点。 1. That the earth travels round the sun is a well-known fact. 2. Whether the artist can do it or not is uncertain. 3. Who will act the lead in the play has not been decided yet. 4. Where the young man has gone is not known. 5. When and where the test will be given is not yet decided. 【归纳总结】主语从句必须有引导词；主语从句用陈述句语气。 1. 引导主语从句的词有： 连词: that, whether； 连接代词: who, whose, whom, whoever, what, which等； 连接副词where, when, whenever, wherever, how, why等。 主语从句引导词的选择： 1).连接词: that, whether (1) That he will win is certain. (2) It has been reported that sales of beef in China will increase. (3) Whether we shall raise ducks or geese remains to be decided. (4) Whether he ’ll join us in the discussion is of great importance. 2) 连接代词: who, whom, whose, what, which, whoever, whatever, whichever 等。 (1) It is clear who is afraid of having a change in land ownership. (2) Whose bag it is cannot be told. (3) What India needs is a law to make land ownership fairer. (4) It is not yet decided which cash crop will be produced next year. (5) Whatever he said was right.
高中英语语法主语从句 第一节主语从句 1．考点解析。 1．主语从句一般分为三类：由what等代词引导的主语从句；由连词that 引导主语从句，多数情况下由it作形式主语，that从句放到句子后面去；由连接代词或连接副词（或whether）引导的主语从句。 What they are after is beauty. It is not your fault that we can’t arrive on time. When they will arrive has not been decided. 2. 由关系代词what引导的主语从句，也可由whatever（“所…的一切”）或 whoever（“一切…的人”）引导。 Whatever he wants is your support. Whoever comes will be welcome. 3. 大多数主语从句都可用it代替，作形式主语，把主语从句放在句尾。要注意it代替主语从句和it引导的强调句的区别。强调句的结构是it is/was….+that…，强调人是可把that 换做who，whom，whose。如强调的是状语时，也只能用that,而不能用when, where, how, why等。 It was in Paris that they fell in love with each other. It is the lady who was my English teacher. It was last semester that he won the first prize. 2. 试题详解。 1．______ he needs is more experience. A. Who B. That C. What D. How 2.It was because of the heavy snow ______ the train was late. A. why B. that C. so D. thus 3．It doesn’t matter ______ he likes or not. A. whether B. what C. when D. that 4______ he has won the Noble Prize has been proved to be true. A. What B. How C. It D. That 5．What he wants _______ to sleep more. A. are B. have been C. is D. were 6．______ we can begin this investigation is still a question. A. When B. Why C. What D. That 7．It is ______ that the highway will be open to traffic nest year. A. report B. reported C. reporting D. by report 8．______ fails to see this will make a big mistake. A. Whatever B. what C. wherever D. Whoever 9．It is a mystery _____ the prisoner escaped. A. why B. how C. what D. that 10．It was last summer _____ he graduated from the college. A. that B. when C. / D. where 3. 实战演练。 1. We didn’t know ______ she didn’t come. A. why B. that C. when D. it 2. It is still doubtful _______ she would play the part.
高考英语主语从句 定义：用作主语的从句叫主语从句，它是名词性从句之一。主语从句的时态：不受主句的时态影响和限制。引导主语从句的连接词有： 从属连词: that, whether； 连接代词: who (whoever), whom, whose, what (whatever)和which (whichever)； 连接副词: when, where, how和why。 连接词： 1. 从属连词：that，whether 1）that引导主语从句只起引导作用，在主语从句中不充当任何成分，that本身无实际意义，但不能省略。2）whether意为“是否”，放在句首句末皆可。由whether引导的名词从句做主语，表语，介词宾语，同位语时！不可用if代替。 a.That price will go up is certain. b. Whether they would support us was a problem. 他们是否会支持我们还是一个问题。 2. 连接代词who ，what ，which, whatever, whichever, whoever (Who, whom, which, what可以和ever构成合成词，和what一样引导从句，ever起到强调作用。此类主语从句不能用形式主语it引导，它们在句子中担任成分，不能省略，语序为陈述语序，既有疑问含义,又起连接作用,同时在从句中充当各种成分。 Which side will win is not clear. Whoever breaks the law will be punished. Whatever he did is right. Who killed the scientist remains a question. 1）What和that引导的主语从句的区别：that 只起引导作用，不充当任何成分，没有意思。What 不仅起引导作用，还要充当一定成分(主语、宾语或表语)，意思是：“什么”。 What we need is money. That he will come is certain. 2）whatever / whoever的用法（~ever=no matter ~---让步状语从句中） whatever / whoever可以引导主语从句,并在句中作主语、宾语、表语等,不含疑问意义。whatever相当于anything that; whoever 相当于anyone who。例如: Whoever(Anyone who) wants to enter into this school must take the exam. Whatever(Anything that) she did was right. 3. 连接副词when，where，how，why等。既有疑问含义,又起连接作用,同时在从句中充当各种成分。How this happened is not clear to anyone. When he will be back depends on the weather. When we’ll start tomorrow will be told soon. Where the test will be given is not yet decided. 4. 主语从句后置：为了避免主语冗长,句子头重脚轻,经常用it 作形式主语,主语从句放在后面作真正的主语. 例: That we shall be late is certain. -- It’s certain that we shall be late. 1）用it 作形式主语的结构 A. It + be + 形容词+ that 从句 (obvious, true, surprising, good, wonderful, funny, possible, likely, certain, probable, etc.) 如：It is certain that she will do well in her exam. B. It + be + 名词词组+ that 从句(an honour, a fact, a pity, etc）如： It is a pity/shame that... 遗憾的是…… It is a surprise that…令人惊奇的是… It is a fact that… …是事实It is common knowledge that… …是常识 It’s a pity that we can’t go. C. It + be + 过去分词+ that 从句(said, reported, thought, expected, decided, announced, etc。）如：It is said that Mr. Green has arrived in Beijing. D. It + 不及物动词或短语+ that 从句( seem，happen, doesn’t matter ,turn out）。如： It happened that I was out that day. It doesn’t matter whether she will come or not. 2) 对于以连接代词(副词)引导的主语从句,可以使用形式主语代主语从句,也可直接在句首使用主语从
语法要点剖析 一、名词性从句 主语从句、表语从句、宾语从句、同位语从句，在整个句子中所起的作用，相当于一个名词。因此，这四种从句通称为名词性从句。 引导名词性从句的连接词可分为三类： 连接词：that, whether, if （不充当从句的任何成分） 连接代词：what, whatever, who, whoever, whom, whose, which. 连接副词：when, where, how, why 1. 主语从句 作句子主语的从句叫主语从句。主语从句通常由从属连词that，whether，if 和连接代词what，who，which，whatever，whoever以及连接副词how，when，where，why等词引导。that在句中无词义，只起连接作用；连接代词和连接副 词在句中既保留自己的疑问含义、又起连接作用，在从句中充当从句的成分。例如： What he wants to tell us is not clear. 他要跟我们说什么，还不清楚。 It is known to us how he became a writer. 我们都知道他是如何成为一名 作家的。 Where the English evening will be held has not yet been announced. 英语晚会将在哪里举行，还没有宣布。 有时为避免句子头重脚轻，常用形式主语it代替主语从句作形式主语放于句首，而把主语从句置于句末。主语从句后的谓语动词一般用单数形式。常用句型如下： （1）It + be + 名词+ that从句（2）It + be + 形容词+ that从句 （3）It + be + 动词的过去分词+ that从句（4）It + 不及物动词+ that 从句 另注意在主语从句中用来表示惊奇、不相信、惋惜、理应如此等语气时，谓语动词要用虚拟语气“(should) +do”，常用的句型有： It is necessary (important, natural, strange, etc.) that … It is a pity (a shame, no wonder, etc.) that… It is suggested (requested, proposed, desired, etc.) that… 2. 宾语从句 名词句用作宾语的从句叫宾语从句。引导宾语从句的关联词与引导主语从句表语从句的关联词大致一样，在句中可以作谓语动词或介词及非谓语动词的宾语。 1. 由连接词that引导的宾语从句 由连接词that引导宾语从句时，that在句中不担任任何成分，在口语或非正式的文体中常被省去，但如从句是并列句时,第二个分句前的that不可省。例如：He has told me that he will go to Shanghai tomorrow.他已经告诉我他明天要去 上海。 We must never think (that) we are good in everything while others are good in nothing. 我们决不能认为自己什么都好，别人什么都不好。
主语从句( if除外) 一定义：在复合句中充当主语的句子，叫主语从句；位于句首。 二：读例句，理解句意，思考，分析，总结。 1：连接词that 引导的主语从句： EG:1）That you are so angry bothers me. 你如此生气使我很烦恼。 2）That she survived the accident is a miracle.她在事故中幸免于难简直是奇迹。 3）It was a pity (that) you didn’t go to the talk.很遗憾你没有去听报告。 4）That he has moved to New York is not true.= It is not true that he has moved to New York. 5）That the earth is round is true.= It is true that the earth is round. 总结：在连接词that 引导的主语从句中，that ___含义，在句子___做成分，__省。EX: 1)______ he will succeed is certain. 2) ________ you didn’t go to the park was a pity. 3) ______ you will win the medal seems unlikely. 2: 连接词whether引导的主语从句。 EG: 1）Whether wild life can be well protected is of great importance. 2）Whether Mary really heard him is really doubtful. 3）Whether it will do us harm remains to be seen. 是否对我们有害还要看一看。 4）Whether he will come hasn’t been decided.= It hasn’t been decided whether he will come. 总结：在连接词whether 引导的主语从句中，whether__含义，____做成分，__ 省。EX: 1) ______ she is coming or not doesn’t matter too much. 她来不来都无关紧要。 2) ______ they would support us was a problem. 他们是否会支持我们还是一个问题。 3) _______ to hold the meeting has not been discussed. 3：在连接代词（who,whom,whose,which,what,whoever,whomever,whichever,whatever）引导的主语从句中。 EG: 1）What is needed for the space trip is careful preparation. 2）Who will be sent to carry out the task has been settled. 3）Whom she borrowed money from still puzzled me. 4）Which side will win is not clear. 5）What I want to know is this. 6）Whoever breaks the law will be punished.( _____ 从句) = Anyone who breaks the law will be punished . ( _____ 从句) 比较：Whoever breaks the law , he should be punished. ( _____ 从句) = No matter who breaks the law, he should be punished. ( _____ 从句) 总结：在连接代词引导的主语从句中，连接代词__含义，___成分，做___语、___语、___语，_____ 省。
It + be + adj.+ that... 主语从句中常见的一种形式，即以引导词that引出的主语从句，常以形式主语it 代替。主语从句的时态不受主句的时态影响和限制，根据句子意思用适当的时态。结构：It is+adj.+that从句。常用于这个句型的形容词有：necessary, important, clear, strange, true, good, wonderful, possible, unusual, certain, surprising; interesting等。 根据汉语意思完成句子。 1．他可能已经把一切都告诉她了。 ____ is possible that he ____ ____ her everything. 2．海怪突然出现了很奇怪。 It ____ _____ that sea monsters suddenly ___________. 3．毫无疑问她将会在测验中做得很好。 It is certain _____ she ____ ____ well in her exam. 用适当的形容词填空 1. Miss Li often says that it is ________ to learn a foreign language well. 2. Look at the black clouds in the sky. It is ________ to rain soon. 3. It is ________ that Sunday is the first day of the week. 4. Isn’t it ________ that chickens can swim? 5. Is it ________ the lazy boy can catch up with all his classmates? 很多形容词可以与介词连用。我们已学过很多这样的搭配，现在一起来复习一下。形容词与某个特定的介词连用，表示某个特定的意思。 ①与about连接的形容词：be worried about“担心……”；be excited about“对……感到兴奋”；be careful about“小心、谨慎”；be mad about“狂热地迷恋”；be anxious about “为……感到焦虑”；feel nervous about/ at“对……感到心神不安”。 ②与at连接的形容词：be shocked at“对……感到震惊”；be good at“擅长……”；be bad at“在某方面不好或坏”；be angry at/ about sth“对……生气”；be mad at sb“对……发怒”；be surprised at“对……感到惊讶”。 ③与as连接的形容词：be famous/ known as“作为……而著名”；be known as “被叫作……”。 ④与for 连接的形容词：be good for“对……有好处”；be bad for“对……有害”；be afraid for“为……而担心”；be famous / known for sth“因……而著名”；be mad for “渴望”；be happy for“为……感到高兴”；be responsible for“负责，有责任”；be free for“对……免费”；be available for“有空的”；be thankful for“感谢，感激……”；be ready for“为……做准备”。 ⑤与from 连接的形容词：be different from“与……不同”。 ⑥与of 连接的形容词：be short of“缺乏……”；be afraid of“害怕……”；be unaware of “没意识到……，不知道……”；be tired of“厌倦，厌烦……”；be proud of“为……感到自豪”；be full of“充满……的”。 ⑦与on 连接的形容词：be based on“基于，根据”；be keen on“喜爱”；be dependent on “依靠”。
一、主语从句的引导词 主语从句通常由连词that和whether、连接代词或连接副词以及关系代词型what引导。 1. that引导 That he is still alive is a wonder. 他还活着，真是奇迹。 That we shall be late is certain. 我们要晚了，这是确定无疑的 That he should have ignored the working class was natural. 他忽视工人阶级是很自然的。That she is still alive is a consolation. 她还活着是使人感到宽慰的。 That she became an artist may have been due to her father’s influence. 她成为画家可能是受她父亲的影响。 That you are coming to London is the best news I have heard this long time. 你将来伦敦是好久以来我听到的最好消息。 That she was chosen made a tremendous stir in her village. 她被挑选上，在她村子里引起很大轰动。 2. whether引导 Whether it will do us harm remains to be seen. 是否对我们有害还要看一看。 Whether they would support us was a problem. 他们是否会支持我们还是一个问题。 3. 连接代词引导 Whoever is top from wins the game , when two matched players meet. 两强相争勇者胜。Whichever (of you) comes in first will receive a prize. 无论(你们)谁先到都可以得奖Whichever you want is yours. 你要哪个,哪个就是你的。 4. 连接副词引导 When we arrive doesn’t matter. 什么时候到没有关系。 How it was done was a mystery. 这是怎样做的是一个谜。 How this happened is not clear to anyone. 这件事怎样发生的，谁也不清楚。 How many people we are to invite is still a question. 邀请多少人还是一个问题。 Where I spend my summer is no business of yours. 我在哪里过暑假不关你的事。 5. 关系代词型what引导 What we need is money. 我们需要的是钱。 What I want to know is this. 我想知道的就是这一点。 What’s done is done. 事已成定局。 What he says is not important. 他说的话并不重要。 What I am telling you is mere impressions. 我和你说的都不过是一些印象而已。 What make the river more beautiful are the lotus plants growing in the water. 为河水增色的是水里的荷花。 What you need is a good-sized canvas bag. 你需要的是一个比较大的帆布袋。 What I am afraid of is their taking him to Portugal. 我担心的是他们把他带到葡萄牙去。What struck me was that they have all suffered a lot. 给我很深印象的是他们都受过很多苦。 二、主语从句与形式主语it 有时为了考虑句子平衡，通常在主语从句处使用形式主语it，而将真正的主语从句移至句末。这分三种情况： (1) 对于以连词that引导的主语从句，通常用形式主语代主语从句： It’s a pity that he didn’t come. 很遗憾他没来。 It is important that he should know about this. 他必须知道此事。 It’s vital that we be present. 我们出席是至关重要的 It was intended that you be the candidate. 大家的意图是让你当候选人。 It is important that this mission not fail. 这项使命不失败至关重要。 It is essential/indispensable that a meeting be convened this week. 本周开一次会非常重要。 It is appropriate that this tax be abolished. 废除这个税是恰当的。 It’s unfair that so many people should lose their jobs. 竟有这么多人失业这是不公平的。It’s amazing that she should have said nothing about it. 她竟未谈及此事令人惊讶。 It’s unthinkable that they should deny my request. 他们竟然拒绝我的请求，这是不可思议的。 That they should refuse to sign the petition required great courage. 他们拒绝在请愿书上签字这是需要很大勇气的。 3.有时为避免句子头重脚轻，常用形式主语it代替主语从句作形式主语放于句首，而把主语从句置于句末。主语从句后的谓语动词一般用单数形式。常用句型如下： （1）It + be + 名词 + that从句
as的用法: (as引导定语从句,在定语从句中作主语、宾语、表语) (1)如为限制性的，多用于the same …as ; the same as；such …as …; as many/muchas；so …as等结构中。如： 1. I have the same book as you (have).我有一本和你的一样的书。 Her attitude to him was quite the same as it had always been. (关系代词as和指示代词same连用,在从句中用作表语,先行词是same.) 2.---Why didn't you mention that in face of the police just now? --- I thought it was such a minor detail as was hardly worth mentioning. We will only discuss such problems as have something to do with our own interests.Don't do such things as you are not sure about. There is no such place as you dream of in all this world. 比较： I live in the same house that he used to live in. I'm wearing the same shirt as you wore yesterday. 比较： Here is so big a stone as no one can lift.（定语从句） Here is so big a stone that no one can lift it.（结果状语从句） (2)如为非限制性的，多单独引导一个定语从句，这种定语从句可置于句首，句中或句尾，译为"正如，这一点"。（动词常为know, see, expect, point out, etc.） 1. As we all know, smoking is harmful to one's health . (as作宾语) =As is known to all, smoking is harmful to one's health .（as作主语）