江苏注册会计师:2011年冲刺高考语法讲解与练习 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

主语从句

一、主语从句的概念与类型

　　主语从句在复合句中作主句的主语,引导主语从句的词有从属连词that, whether以及连接代词who, what, which, whoever, whatever, whichever和连接副词when, where, why, how等.例如:

　　That she was chosen made us very happy.她当选了使我们很高兴.

　　What caused the accident is a complete mystery.是什么导致了这次事故还完全是一个谜.

　　Whether she will come or not is still a question.她是否来还是一个问题.

　　Which team will win the match is still unknown.哪个队会赢得这场比赛还不知道.

　　Whoever comes to the party will receive a present.参加聚会的每一个人都将收到一份礼物.

　　When they will start has not been decided yet.他们何时出发还没决定.

　　注意:上述例句中的主语从句都是放在句首,但有时为了使句子结构平衡,避免"头重脚轻",常用it作形式主语,而把从句放在后面.例如:

　　It is a pity that she has made such a mistake.她犯了这样一个错误,真是遗憾.

　　It depends on the climate whether they are going shopping today.他们是否今天去购物还得看天气情况.

　　这样就构成了下面一些常用句型:

　　1)It is + adj. / n. +从句

　　It is a pity/shame that...遗憾的是……

　　It is possible that...很可能……

　　It is unlikely that...不可能……

　　2)It +不及物动词+从句

　　It seems/appears that...似乎……

　　It happened that...碰巧……

　　3)It + be +过去分词+从句

　　It is said that...据说……

　　It is known to all that...众所周知……

　　It is reported that...据报道……

　　It is believed that...据信……;人们相信……

　　It is suggested that...有人建议……

　　It must be pointed out that...必须指出……

　　It has been proved that...已证明…….例如:

　　It is believed that at least a score of buildings were damaged or destroyed.据信,至少有二十座楼房遭到破坏或彻底毁掉.

　　It is suggested that the meeting should be put off.有人建议会议延期召开.

　　It's reported that three people were killed in the accident and five were hurt badly.据报道,事故中三人丧生,五人重伤.

　　It is known to all that Taiwan is an inseparable part of China.众所周知,台湾是中国不可分割的一部分.

　　[巩固练习]

　　1. Does _______ matter if he can't finish the job on time?

　　A. this B. that C. he D. it

　　2. It worried her a bit _______ her hair was turning grey.

　　A. which B. that C. if D. for

　　3. _______ is a fact that English is being accepted as an international language.

　　A. There B. This C. That D. It

　　二、学习主语从句应该注意的几个问题

　　1)引导词that与what

　　what既有引导主语从句的作用,同时又在从句中作句子成分(主语、宾语、表语等).这时what相当于all that/everything that...,常译成"所……的(东西、事情、话等.)";而that只起连接作用,本身无实际意义,在从句中也不担当任何句子成分.但that引导的主语从句放在句首时,不能省略that.例如:

　　What is done can't be undone. (谚语)已成定局,无可挽回.

　　What we can't get seems better than what we have.我们得不到的东西似乎比已得到的要好.

　　That we should work out a plan to deal with the present serious situation is important.我们应该制定一项计划来应付目前严峻的形势,这一点非常重要.

　　That a new teacher will come to teach us geography is true.一位新老师将来教我们地理,这是真的.

　　[巩固练习]

　　4. _______ what they told me really true?

　　A. Has B. Is C. Does D. Have

　　5. It matters little _______ a man dies, but _______ matters much is _______ he lives.

　　A. how; what; how B. how; it; how C. why; it; why D. that; what; that

　　6. _______ she couldn't understand was _______ fewer and fewer students showed interest in her lessons.

　　A. What; why B. That; what C. What; because D. Why; that

　　7. It is pretty well understood _______ controls the flow of carbon dioxide in and out the atmosphere today.

　　A. that B. when C. what D. how

　　8. _______ fashion differs from country to country may reflect the cultural differences from one aspect.

　　A. What B. That C. This D. Which

　　9. -What made her parents so angry?

　　- _______ she had failed in the examination.

　　A. As B. Because C. Since D. That

　　2)引导词if和whether

　　if和whether引导动词后的宾语从句时一般可通用,但介词后的宾语从句、主语从句(放在句首时)、表语从句常由whether引导.例如:

　　Whether she will go home or not is unknown.她是否回家还不得而知.

　　Whether we shall raise ducks or geese remains to be decided.我们是养鸭还是养鹅仍没决定.

　　=It remains to be decided whether/if we shall raise ducks or geese.

　　但我们不能说If we shall raise ducks or geese remains to be decided.

　　[巩固练习]

　　10. _______ we'll go camping tomorrow depends on the weather.

　　A. If B. Whether C. That D. Where

　　3)其它引导词

　　连接代词who, which, whom, whose有各自的意义,起连接作用,并在从句中充当语、宾语、表语、定语等;连接副词when,where, why, how等有各自的意义,起连接作用,并在从句中充当状语.

　　[巩固练习]

　　11. -Do you remember _______ he came?

　　-Yes, I do. He came by car.

　　A. how B. when C. that D. if

　　12. It was a matter of _______ would take the position.

　　A. who B. whose C. whom D. whomever

　　13. -I drove to Zhuhai for the air show last week.

　　-Is that _______ you had a few days off?

　　A. why B. when C. what D. where

　　14. I read about it in some book or other, does it matter _______ it was?

　　A. where B. what C. how D. which

　　三、语气

　　在It is necessary / natural / important / strange...+ that-clause这类句型里,that所引导的主语从句中谓语动词用"should +原形",表虚似语气.例如:

　　It is necessary that the problem should be settled at once.这个问题必须马上解决.

　　It's strange that he should have gone away without telling us.他竟然没向我们说一声就走了,真是奇怪.

　　[巩固练习]

　　15. It is necessary that a college student _______ at least a foreign language.

　　A. masters B. should master C. mastered D. will master

　　四、以it作形式主语的主语从句与强调句型的区别

　　"It be + adj./n. + that-clause"与强调句型均有It be...that...之类的语言标志,但不同的是:①前者中的that从句是主语从句.若删掉其中的It be和that,则剩余部分不论结构还是语意都不能成为一个句子;但若将后者中的It be和that去掉,则剩余部分的结构和语意仍能构成一个完整的句子.②强调句型译为汉语时可加上"正是……"或"就是……"之类的字眼,而主语从句则不可以.请比较下面两个句子:

　　It is surprising that Mary should have won first place.令人惊奇的是玛莉竟然获得了第一名.

　　It is Mary that has won first place.正是玛莉得了第一名.

　　第一句话中的It是形式主语,that引导的是主语从句.句中的It is和that无法删除,一旦删除句子就不成立.

　　第二句是强调句型,其中的It is和that可以去掉,因为没有It is和that句子仍然很通顺.

　　Key: 1-5 DBDBA 6-10 ACBDB 11-15 AAADB

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。

注意：在demand、order、suggest、decide、insist, desire, demand, request, command等表示要求、命令、建议、决定等意义的动词后，宾语从句常用“（should）+ 动词原形”。例如：

I insist that she (should) do her work alone. 我坚持要她自己工作。

The commander ordered that troops (should) set off at once. 司令员命令部队马上出发。

2. 用who，whom, which, whose, what, when, where, why, how, whoever, whatever, whichever等关联词引导的宾语从句相当于特殊疑问句，应注意句子语序要用陈述语序。例如：

I want to know what he has told you. 我想知道他告诉了你什么。

She always thinks of how she can work well. 她总是在想怎样能把工作做好。

She will give whoever needs help a warm support. 凡需要帮助的人，她都会给予热情的支持。

3. 用whether或if引导的宾语从句，其主语和谓语的顺序也不能颠倒，仍保持陈述句语序。此外，whether与if 在作“是否”的意思讲时在下列情况下一般只能用whether，不用if：

a. 引导主语从句并在句首时；b. 引导表语从句时；c . 引导从句作介词宾语时；d. 从句后有“or not”时；e. 后接动词不定式时。例如：

题。

The question is whether she should have a low opinion of the test?

Everything depends on whether we have enough money. 一切要看我们是否有足够的钱。

I wonder whether he will come or not. 我想知道他来还是不来。

Can you tell me whether to go or to stay? 你能否告诉我是去还是留？

4. 注意宾语从句中的时态呼应，当主句动词是现在时，从句根据自身的句子情况，而使用不同时态。例如：

he studies English every day. （从句用一般现在时）

he studied English last term. （从句用一般过去时）

I know (that) he will study English next year. （从句用一般将来时）

he has studied English since 1998. （从句用现在完成时）

当主句动词是过去时态（could, would除外），从句则要用相应的过去时态，如一般过去时，过去进行时，过去将来时等；当从句表示的是客观真理，科学原理，自然现象，则从句仍用现在时态。例如：

The teacher told us that Tom had left us for America．

5. think, believe, imagine, suppose等等动词引起的否定性宾语从句中，要把上述主句中的动词变为否定式。即将从句中的否定形式移到主句中。例如：

We don’t think you are here. 我们认为你不在这。

I don’t believe he will do so. 我相信他不会这样做。

3. 表语从句

在句中作表语的从句叫表语从句。引导表语从句的关联词与引导主语从句的关联词大致一样，表语从句位于连系动词后，有时用as if引导。其基本结构为：主语 + 系动词 + that从句。

（一）表语从句的引导词

引导表语从句的词有连词that, whether，连接代词和连接副词，关系代词型what，以及as if, as though, because等连词。

1. 由that引导

The fact is that he doesn’t really try. 事实是他没有做真正的努力。

The trouble is that I have lost his address. 麻烦的是我把他的地址丢了。

My suggestion is that we should tell him. 我的建议是我们应该告诉他。

His sole requirement was (is) that the system work. 他唯一的要求是这个制度能起作用。

My idea is that we should start making preparations right now. 我的意见是我们马上就开始做准备工作。

2. 由whether引导

The question is whether the film is worth seeing. 问题是这部电影是否值得看。

【注意】whether 可引导表语从句，但与之同义的if却通常不用于引导表语从句。

3. 由连接代词引导

You are not who I thought you were. 你已不是我过去所想像的人。

The problem is who we can get to replace her. 问题是我们能找到谁去替换她呢。

The question is who (m) we should trust. 问题是我们应当相信谁。

What I want to know is which road we should take. 我想知道的是我们应走哪条路。

4. 由连接副词引导

The problem is how we can find him. 问题是我们如何找到他。

That was when I was fifteen. 这是我15岁时发生的事。

That’s where I first met her. 那就是我第一次遇见她的地方。

That’s why he didn’t come. 这就是他没有来的缘故。

That’s why I object to the plan. 这就是我反对这个计划的原因。

That’s where you are wrong. 这就是你不对的地方。

5. 由关系代词型what引导

That’s what I want to stress. 这是我想强调的。

That’s what we are here for. 我们来这里就为了这个。

Fame and personal gain is what they’re after. 他们追求的是名利。

He is no longer what he was. 他已经不是以前的他了。

6. 由as if / as though引导

It isn’t as if you were going away for ever. 又不是你离开不回来了。

Now it was as though she had known Millie for years. 现在好像她认识米莉已有好多年了似的。

It is not as though we were poor. 又不是我们家里穷。

7. 由because引导

It is because I love you too much. 那是因为我太爱你了。

That’s because you can’t appreciate music. 这是因为你不能欣赏音乐。

If I’m a bit sleepy, it’s because I was upall night. 如果我有点困，是因为一夜没睡。

It's because I passed a slip of paper for John to Helen in class. 这是因为我在上课中替约翰传纸条给海伦。

【注意】because 可引导表语从句，但与之同义的since, as, for等也不用于引导表语从句。

（二）、连词that的省略问题

引导表语从句的that通常不省略，但在口语或非正式文体中有时也可省略：

My idea is (that) we should do it right away. 我的意见是我们应该马上干。

4. 同位语从句

同位语从句说明其前面的名词的具体内容。同位语从句通常由that引导，可用于同位语从句的名词有advice、demand、doubt、fact、hope、idea、information、message、news、order、problem、promise、question、request、suggestion、truth、wish、word等。

）一）、同位语从句的引导词

引导同位语从句的词语通常有连词that，whether，连接代词和连接副词等。

1. 由that引导

We heard the news that our team had won. 我们听到消息说我们队赢了。

They were worried over the fact that you were sick. 他们为你生病发愁。

The news that we are having a holiday tomorrow is not true. 明天放假的消息不实。

I’ve come to the conclusion that it was unwise to do that. 我得出结论这样做是不明智的。

The fact that the money has gone does not mean it was stolen. 那笔钱不见了这一事实并不意味着是被偷了。

He referred to Copernicus’ statement that the earth moves round the sun. 他提到了哥白尼关于地球绕太阳转的说法。

【注意1】 在某些名词(如demand, wish, suggestion, resolution等)后面的同位语从句要用虚拟语气。如：

They were faced with the demand that this tax be abolished. 他们面对废除这个税的要求。

They expressed the wish that she accept the award. 他们表示希望她接受这笔奖金。

There was a suggestion that Brown should be dropped from the team. 有一项建议是布朗应该离队。

The suggestion that the new rule be adopted came from the chairman. 采纳新规则的建议是主席提出的。

The resolution that women be allowed to join the society was carried. 允许妇女参加这个协会的决议通过了。

I can understand their eagerness that you should be the main speaker. 我理解他们希望你作主要发言人的殷切心情。

【注意2】 引导同位语从句的连词that通常不省略，但在非正式文体中也可以省去。如：

He gabbed his suitcase and gave the impression he was boarding the Tokyo plane. 他拿起了手提箱，给人的印象是他要登上飞往东京的飞机了。

2. 由whether引导

There is some doubt whether he will come. 他是否会来还不一定。

Answer my question whether you are coming. 你回答我的问题：你来不来。

The question whether it is right or wrong depends on the result. 这个是对还是错要看结果。

We are not investigating the question whether he is trustworthy. 我们不是在调查他是否可以信任的问题。

【注意】  whether 可引导同位语从句，但if不能引导同位语从句。

3. 由连接代词引导

Have you any idea what time it starts? 你知道什么时候开始吗?

From 1985-90 I was an instructor at the regional party headquarters. After that I went back to work in a factory. Then I had no idea what a casino was. 从1985年到1990年我是地方党部的教员。随后我回到一家工厂工作。当时我不知道赌场是什么样的地方。

4. 由连接副词引导

I have no idea when he will come back. 我不知道他什么时候回来。

It is a question how he did it. 那是一个他如何做的问题。

He had no idea why she left. 他不知道她为什么离开。

You have no idea how worried I was! 你不知道我多着急!

（二）、关于分离同位语从句

有时同位语从句可以和同位的名词分开。如：

The story goes that he beats his wife. 传说他打老婆。

The news got about that he had won a car in the lottery. 消息传开说他中彩得了一辆汽车。

The rumour spread that a new school would be built here. 谣传这里要盖一所新学校。

Report has it that the Smiths are leaving town. 有传言说史密斯一家要离开这座城市。

The thought came to him that maybe the enemy had fled the city. 他想到可能敌人已逃离这座城市。

The order soon came that all citizens should evacuate the village. 不久命令下来，所有居民都必须撤出村子。(

二. 名词性从句中的虚拟语气

1.主语从句中的虚拟语气主语从句中的虚拟语气主要取决于某些形容词和过去分词，用来表示建议、命令、要求、惊异和失望等。

其形式为：（should）+动词原形。

常这样用的形容词有： appropriate适当的advisable适当的，合理的better较好的desirable理想的essential精华的imperative迫切的important重要的insistent坚持的natural自然的necessary必要的preferable优越的，较好的strange奇怪的urgent紧迫的vital极其重要的过去分词有： desired, demanded, ordered, requested, suggested, recommended, required等。

例如：

It is essential that you (should) win the voters’hearts.赢得选民的心是绝对必要的。

It was suggested that he (should) join the club activities.有人提议他应该参加俱乐部的活动。

2.表语从句和同位语从句中的虚拟语气在表示建议、命令、主张、目的和愿望等名词后面的表语从句和同位语从句中谓语动词要求使用虚拟语气。

其形式为：（should）+动词原形。

常这样用的名词有： resolution决心，决议pray恳求decision决议motion提议suggestion建议preference选择proposal提议advice劝告recommendation推荐desire愿望demand要求requirement要求order命令necessity必要性request要求idea主意、想法

He gave orders that the guests (should) be hospitably entertained.他下令热情款待这些客人。

His proposal is that we (should) get rid of the bad habits.他提议我们应该摈弃这些不良习性。

3.宾语从句中的虚拟语气

1）某些动词后所接宾语从句中的谓语动词要求用虚拟语气，用来表示建议、命令和要求等。

其形式为：（should）+动词原形。

常这样用的动词有： ask要求 advise劝告 determine决定 decide决定command命令 insist坚持 intend打算 move提议 prefer宁愿 propose提议 order命令 recommend推荐 request要求 require要求 suggest建议 urge主张 demand要求 desire渴望 direct命令  

例如：

He insisted that the meeting be put off.他要求推迟那个会议。

They proposed that all the plans should be discussed at the meeting.他们建议所有的计划都应该在会上讨论。

2）在以it为形式宾语的复合宾语从句中也可以用虚拟语气，

其形式为：（should）+动词原形。这一句型中使用的形容词（宾补）与主语从句中的虚拟语气所使用的形容词相同。

例如：

We think it advisable that he (should) think deeply before acting.我们认为他在行动之前好好考虑一下才是明智的。

3）wish后面所跟的宾语从句中的虚拟语气表示某种不能实现的愿望。

其主要形式有三种：

表示对现在情况的虚拟：wish +主语+动词过去式或were表示对过去情况的虚拟：wish +主语+ had +过去分词表示对将来情况的虚拟：wish +主语+ would +动词原形。

例如：

I wish I knew what was going to happen.但愿我能知道要发生什么事。

She wished she had stayed at home.她懊悔的是她当时要是在家就好了。

I wish I were rich.我恨不得我很有钱。

注意：在表示对过去情况的虚拟时，有时也可以用下列形式：

wish +主语+ would（could）+ have +过去分词I wish I could have seen her last night.要是我昨天晚上能够见到她那该多好。

4. if条件句中的虚拟语气形式1）if非真实条件句所表示的假设则是不可能或不大可能发生或实现的，句中的主句与从句都用虚拟语气。

在if非真实虚拟条件句中，主句和从句谓语动词主要有下面几种形式：假设类型条件从句谓语动词形式主句谓语动词形式与现在事实相反动词过去时（be用were）Should（would，could，might）+动词原形与过去事实相反Had +过去分词Should（would，could, might）+ have +过去分词与将来事实可能相反动词过去时（should+动词原形，were to +动词原形）Should（would，could，might）+动词原形

If there were no gravity, we should not be able to walk.假如没有引力，我们就不可能行走。

I wouldn’t have known what these were for if I hadn’t been told.假如别人不告诉我，我就不知道这些东西是干什么的了。

2）正式文体中，有时可把虚拟条件句中的连词if省去，而将were，had, should等助动词（不包括行为动词）提到主语前面。如果句中没有were，had或should时，既不能省略if，也不能倒装。例如：

Were I to meet him tomorrow (= If I were to met him tomorrow), I should ask him about it.要是我明天见到他，我就会问他这件事的。

Had I had the money last year (= If I had had the money last year), I would have bought the house.如果我去年有了这笔钱，我就买那所房子了。

Should there be any trouble with the boiler, the automatic controlling unit would cut off the fuel oil supply.假如锅炉出问题的话，自控装置会自动切断燃油的供给。

3）通常情况下，在非真实条件句中主句和从句的谓语动词所指时间是一致的，但有时也可能指不同的时间，这时要根据上下文的意思采用不同的谓语动词形式。例如：

If I were you, I would have taken his advice.我要是你，我就采纳了他的建议。（从句指现在，主句指过去）

If the weather had been more favorable, the crop would be growing still better.如果气候更适宜一些，庄稼会长得更好。（从句指过去，主句指现在）

5.含蓄虚拟条件句1）有时假设的情况并不以条件从句形式表示出来，而是通过一个介词短语或其他方式表示。常用的词或短语有：without, but for, but that, otherwise, or, but等。例如：

Without your help (=If we had not had your help), we could not have succeeded.要是没有你的帮助，我们就不会成功的。

But for electricity (= If there were no electricity), there would be no modern industry.要是没有电，就不会有现代工业。

He was having a meeting; otherwise he would have come over to help us.他当时正与他的学生进行讨论，否则的话他就来帮我们了。

He felt very tired yesterday, or he would have attended the party.他昨天很累，不然他就参加那个聚会了。

2）在某些暗含虚拟条件的简单句中，虚拟语气可通过上下文表现出来。谓语动词用should/ would be形式和should/ would have been虚拟形式。例如：

Any men in his position would have done like that.任何人处在他的位置都会那么做的。

You should (ought to) have come earlier.你本应来得早点。

6.其他句型中的虚拟语气1）在would rather, would sooner, would just as soon, might as well和would prefer等后面所跟的从句中，也可以用虚拟语气，表示愿望，意为“宁愿、但愿”。其形式为：

①“would rather (would sooner…) +主语+谓语动词过去式”表示现在或将来的情况。

②“would rather (would sooner) +主语+动词过去完成式”表示过去的情况。例如：I’d rather he didn’t go now.要是他现在不走就好了I’d just as soon you had been here yesterday.要是你昨天在这里就好了。

2）在句型“It is (high/ about) time…”后面也可以跟虚拟语气，从句中常用过去式。有时也用“（should）+动词原形”，意为“该是……的时候了”。例如：

It is time that the boy (should) go to school.这个小孩该上学了。

It is high time (that) the weather improved.天气真该好起来了。

3）在“if only”引起的感叹句中也要求用虚拟语气，表示愿望。

形式为：①用过去时或“would/ could +动词原形”表示与现在或未来事实相反的愿望。

②过去完成时表示与过去事实相反的愿望。例如：

If only you would listen to our advice.要是你听我们的建议就好了。

If only I had not been busy last week!要是上周我不忙该多好啊！

If only she could marry me.但愿她能嫁给我。

注：if only也可以用于虚拟条件句中。例如：

If only I had more money, I could buy a car.要是我有更多的钱，我就可以买辆车了。

4）连接词“in case, lest, for fear that”可以用来引导虚拟语气。其形式通常为：“…lest (in case, for fear that) +主语+ should +动词原形”。Lest, for fear that句中的should可以省去，in case句中的should通常不省去，但是in case句中可以不用虚拟语气，而用陈述语气。Lest, for fear that后面也可以接其他形式。例如：

He took his coat with him in case it should rain.他带着雨衣以防下雨。

I will not make a noise for fear that I (should/ might) disturb you.我不会做声的，以免打扰你。

Care must be taken in using this method lest overflow (should) occur.在使用这以方法的时候要谨慎小心，以免发生溢流现象。

同位语从句与定语从句的区别

1．意义的不同

同位语从句是用于说明所修饰名词的具体内容的，它与被修饰词语通常可以划等号；而定语从句是限制所修饰名词的，它的作用是将所修饰的名词与其他类似的东西区别开来：

We are glad at the news that he will come. 听到他要来这个消息我们很高兴。(news的内容就是that he will come，故that引导的是同位语从句)

We are glad at the news that he told us. 听到他告诉我们的这个消息我们很高兴。(that从句是限制the news的内容的，即我们高兴只是因为他告诉的这个news而不是其他的news，故that从句为定语从句)

2. 引导词的不同

what, how, if, whatever 等可引导名词性从句，但不引导定语从句。

3. 引导词的功能上的不同

that引导同位语从句时，它不充当句子成分，而引导定语从句时，它作为关系代词，要么充当定语从句的主语，要么充当定语从句的宾语。如上例 that he told us中的that就充当told的宾语。

4. 被修饰词语的区别

同位语从句所修饰的名词比较有限，通常有hope, wish, idea, news, fact, promise, opinion, suggestion, truth等，而定语从句所修饰的名词则非常广泛。 另外，when和where 引导定语从句时，通常只修饰表示时间和地点的名词，而它们引导同位语从句时却不一定；又如why引导定语从句，它通常只修饰名词the reason，而它引导同位语从句时则不一定：

I have no idea when they will come . 我不知道他们什么时候来。(同位语从句)

I’ll never forget the days when I lived there.. 我永远不会忘记我住在那儿的日子。(定语从句)

We don’t understand the problem why this is the best choice. 我们不明白这个问题，为什么这是最好的选择。(同位语从句 )

The reason why he didn’t come to the meeting is that he is ill. 他未能来开会，原因是他生病了。(定语从句)

The primary reason was skepticism that a railroad built through so challenging and thinly settled a stretch of desert,mountain, and semiarid plain could pay a profit.

同位语从句

主句:The primary reason was skepticism.

that从句做skepticism的同位语，具体说明skepticism.

that从句主干a railroad could pay a profit.其他的都是用来修饰railroad...过去分词短语做后置定语修饰railroad.

常见的同位语从句先行词是news，idea，fact，promise，question，doubt，thought，hope，message，suggestion，words（消息），possibility等。

这些都是抽象名词，你的这个例子中skepticism,怀疑态度也是抽象名词。

同位语从句的特点是，你可以去掉先行词，句子仍然成立，没有语法错误。

这里The primary reason was that a railroad built through so challenging and thinly settled a stretch of desert,mountain, and semiarid plain could pay a profit.无错误。所以原句是同位语从句。

名词性从句专项练习100题

1. His success was because of ________ he had been working hard.

A. that                  B. the fact which                 C. the fact that             D. the fact

2. “Is Mary from New York City” “I don't know _______.”

A. from what city does she come from                     B. from what city she come

C. what city does she come from                             D. what city she comes from

3. ________ makes mistakes must correct them.

A. What                B. That                               C. Whoever                 D. Whatever

4. The reason why I didn't go to Shanghai was ________ a new job.

A. because I got    B. because of getting            C. I got                       D. that I got

5. It worried her a bit ____ her hair was turning grey.

A. while                B. that                                C. if                            D. for

6. Henry killed the dog. I'll ask him why ________.

A. did he do that    B. he did that                       C. he did                      D. he has done so

7. Have you seen Henry lately My boss wants to know ________.

A. how he is getting along                                B. how is he getting along

C. what he is getting along                                D. what is he getting along

8. It is generally considered unwise to give a child ____ he or she wants.

A. however           B. whatever                        C. whichever                      D. whenever