一、连接词的选用
　　
　　引导主语从句的连接词很多，有连词：that, whether, if, as if, as though ;连接代词：what, who, whom, which, whose, whatever, whichever, whoever ;连接副词：when, where, why, how, whenever, wherever .连词只起连接作用，不充当句子成分，连接代词、连接副词在句中充当一定的句子成分。其中考查的重点是难于掌握且易混淆的几个连接词。现列举如下：
　　1.that
　　①It worried her a bit -- her hair wad turning gray .(NMET 92)
　　A. whileB. if C. that D. for
　　② -- is a fact that English is being accepted as aninternational language.(NMET 95)
　　A. ThereB. ThisC. That D. It
　　③ -- you don' t like him is none of my business.(上海 1992)
　　A. whatB. who C. That D. whether
　　以上答案分别为：CDC
　　that引导主语从句时只起连接作用，它本身无具体含义，在从句中不充当任何句子成分。而且当它位于句首时多不能省略。此外，应注意that从句作主语时，常用it作形式主语，而把主语从句移到句子的后面去（如例②）。中学常见it作形式主语的句型有：
　　It is + ad j. / n. + that从句
　　It is + p.p. (said, hoped, reported, known, believed etc.) + that从句
　　例：That he has gone abroad for further education is clear to us all. = It is clear to us all that he has gone abroad for further education.
　　我们都清楚他出国深造去了。
　　It is well known that paper was first made in China.
　　众所周知，纸是中国首先制造的。
　　再看2001年一道高考题：
　　-- is known to everybody, the moon travels round the earth once every month.
　　A. ItB. As C. ThatD. what
　　此题很多考生误选了A或C，其原因是没有注意到逗号的作用。句中逗号已表明该句不是主语从句，而是as引导的非限制定语从句。故答案为B。
　　2. what
　　① -- he said at the meeting astonished everybody present . (NMET 93)
　　A.WhatB. That C. The fact D. The matter
　　②After -- seemed a very long time, I opened my eyes and found myself in bed .
　　A. whatB. when C. that D. which
　　③ -- we can't get seems better than -- we have .(NMET 96)
　　A. What, whatB. What, that C. That, that D. That, what
　　以上答案分别为：AAA
　　what引导主语从句时本身有词义，意为"所......的"，相当于"that thing that ..., all that ..., everything that ..."等，在从句中充当主语、宾语、表语，不能省略。
　　例如：What seems easy to some people seems difficult to others .
　　对某些人好像很容易的事情，对别人可能很困难。（作主语）
　　What we can' t get seems better than what we have .
　　我们不能获得的似乎比我们拥有的更好。（作宾语）
　　3．"疑问词＋ ever"构成的复合连接词不达意与"no matter ＋疑问词"引导从句
　　-- has helped to save the drowning girl is worth praising . (99上海)
　　A. WhoB. The one C. Anyone D. Whoever
　　此题答案为D。
　　"疑问词＋ever"构成的复合连接词（however除外）既可以引导名词性从句（主从、表从、宾从、同位语从句），也可以引导让步状语从句，而"no matter＋疑问词"只能引导让步状语从句。二者引导让步状语从句时可以互换，引导名词性从句时只能用"疑问词＋ever"形式。
　　4.whether与if
　　① -- we' ll go camping tomorrow depends on the weather . (NMET 96)
　　A. lf B. whether C. ThatD. where
　　② -- the 2000 OIympic camnes will be held in Beijing is not known yet.(NMET 96)
　　A. WheneverB. IfC. whetherD. That
　　以上答案分别为：BＣ
　　whether与if含义相同，意为"是否"，虽不担任句子成分，但不可省略。
　　（１）二者在动词后引导宾语从句时，常可互换。
　　（２）动词doubt用在疑问句和否定句中时，宾从的连接词用that而不用if或whether，用在肯定句中时，则用if或whether均可，但不能用that。
　　（３）在下列情况下，名词性从句用whether而不用if ：
　　a.介词后的宾从中b.主从和表从中c.动词不定式前d.动词discuss后的宾从中e.后面紧跟or not时f.由if引导的宾从容易产生歧义时
　　
　　二、语序问题
　　
　　主语从写句的语序为陈述语序。
　　例如：When they will start hasn't been decided.
　　他们什么时候开始还没决定。
　　How he managed to finish this composition in such a short time is a mystery .
　　他如何在这么短的时间内完成这篇作文还是个谜。
　　
　　三、主谓一致问题
　　
　　主语从句作主语时，谓语动词一般用单数形式。但what引导从句时，要根据意义一致的原则来决定谓语动词的数。
　　例如：
　　What was once regarded as impossible has come true .
　　以前被认为不可能的事已变成了现实。
　　Whoever told you to give up smoking was quite true .
　　不论谁告诉你戒烟都是对的。
　　Whether you like him is none of my business .
　　你是否喜欢他与我无关。
　　What we need are more good reading materials.
　　我们需要的是更多的好的阅读材料。
　　What we need is more time .
　　我们需要的是更多的时间。
1. 以what等连接代词引导的主语从句

What you need is more practice. 你需要的是更多的练习。

Whoever wants it may have it. 谁要都可以给他。

同类的连接代词还有：What, who, whom, whose, which, whatever, whoever, whichever

2. 以that, whether从属连词引导的主语从句

It was strange that he had made a mistake. 真奇怪，他竟然错了。

That we need more equipment is quite obvious. 我们需要更多的设备，这是很明显的。

Whether he will join us won't make too much difference.

他是否加入我们，没有太大的差别。

3. 主语从句的引导词that什么时候可以省略

当主语从句不太长时，引导词“that”可以省略

It's clear (that) he has done his best. 很明显他已经尽力而为了。

It's a wonder (that) he didn't fail. 真奇怪，他没有失败。

4. 以when等连接副词引导的主语从句

When they will come hasn't been made public. 他们什么时候来还没有公布。

Where she has gone is not known yet. 她去了哪儿，还不知道。

Why he did it will remain a puzzle for ever. 为什么他做那件事将永远是个谜团。

5. 虚拟语气：主语从句

形容词为necessary, important, impossible, strange, natural, essential时，在“It + be + 形容词或过去分词 + 主语从句”中，主语从句要虚拟。

It is necessary that the problem (should) be discussed at once.

立刻讨论这个问题很有必要。

It is strange that he (should) have so many friends. 太奇怪了，他有那么多的朋友。

6. 主语从句与强调句的区别

注意事项：

1). 在主语从句中，把It was … that去掉之后，就已经完全不像一个句子了。

2). 在强调句中，把It was … that去掉之后，还基本上像个句子。

3). 主语从句有以下的引导词：what, who, whom, whose, which, whatever, whoever, whichever

4). 强调句的引导词只有：that, who。

主语从句：

It was strange that he had made a mistake. 如果把，It was … that 去掉以后，剩下strange he had made a mistake.就不算是句子了。

It is immaterial where or when he goes. 他去何处或者何时去是无关紧要的。

<><>It is said that…, 和It is reported that…这样的结构，后面接的是主语从句：

It is said that he’s got married. 听说他已经结婚了。

强调句：

It was she that had been wrong. 错的是她。（强调主语）如果把，It was … that 去掉以后，剩下she had been wrong.还勉强算的上是一个句子。

It was this novel that they talked about last night. 他们昨晚谈论的是这部小说。（强调宾语）

It was in London that I first saw her. 我是在伦敦第一次见到她的。（强调地点状

二）名词性wh-从句

    由wh-词引导，包括who, whom, whose, whoever, what, whatever, which, whichever等连接代词和where, when, how, why等连接副词。Wh-从句的语法功能除了和that从句一样外，还可充当介词宾语、宾语补语和间接宾语等。

    1．Wh-引导主语从句

    【真题例句】What has happened is that people cannot confess fully to their dreams, as easily and openly as once they could, lest they be thought pushing, acquisitive and vulgar. （2000阅读5)

    【结构分析】本句逗号前为既包含主语从句，又包含表语从句的主句。其中主语部分由what引导的名词性从句充当，表语部分由that引导的名词性从句充当。中间插入的部分as easily and openly as once they could使用了比较结构作状语，修饰前面的动词短语confess fully to their dreams。句末的lest引导了一个虚拟的从句，构成形式是should+do，should被省略。此从句中使用了被动语态be thought，并列的三个形容词pushing, acquisitive and vulgar作补语。

    【参考译文】事实上，人们不能像从前那么轻松公开地坦承自己的梦想，以免被人看作是爱出风头、贪婪和庸俗。

    【真题例句】What is odd is that they have perhaps most benefited from ambition if not always their own then that of their parents and grandparents.（2000阅读5)

    【结构分析】本句是一个主系表结构。what引导主语从句What is odd，在主语从句中充当主语，that they have perhaps most benefited from ambition if not always their own then that of their parents and grandparents是表语从句，注意从句中代词that指代ambition。

    【参考译文】奇怪的是也许已经从雄心壮志中获益最多的正是他们--如果不是他们自己的雄心，那么就是他们父母的和祖父母的。

    【真题例句】What was less visible then, however, were the new, positive forces that work against the digital divide.（2001阅读2）

    【结构分析】该句子中，what引导主语从句What was less visible then，并在主语从句中充当主语。主干表语部分包含由that引导的定语从句that work against the digital divide修饰forces，关系代词that指代forces在从句中作主语。

    【参考译文】然而，一些新的可以防止这种信息差距出现的积极因素在当时并不如现在这样明显。

    【真题例句】What they found, in attempting to model thought, is that the human brain's roughly one hundred billion nerve cells are much more talented-and human perception far more complicated-than previously imagined.（2002阅读2）

    【结构分析】本句的主干What they found is that…被分隔结构in attempting to model thought所作的状语隔开。主语为what引导的名词性从句充当，what在从句中充当宾语。表语为that引导的名词性从句充当，在此从句中，使用了比较结构，破折号之间的部分为对前文he human brain's roughly one hundred billion nerve cells are much more talented的补充说明。

    【参考译文】在试图模仿人类思维的过程中，研究人员发现人类大脑的约一千亿个神经细胞比以前想象得要聪明的多，人类的知觉活动也比以前想象得复杂。

    【真题例句】What we forget-what our economy depends on us forgetting-is that happiness is more than pleasure without pain.（2006阅读4)

    【结构分析】本句子主干为what…-what…-is that…两个what引导主语从句，在主语从句中分别充当宾语，that引导的表语从句happiness is more than…中包含一个比较结构。

    【参考译文】但是我们所忘记的--我们的经济指望我们忘却的--是幸福而不仅仅是没有痛苦的快乐。1. It 作形式主语和it引导强调句的比较

　　It 作形式主语代替主语从句，主要是为了平衡句子结构，主语从句的连接词没有变化。而it引导的强调句则是对句子某一部分进行强调，无论强调的是什么成分，都可用连词that。被强调部分指人时也可用who/whom。例如：

　　a) It is a pity that you didn’t go to see the film.  你不去看那场电影真可惜。

　　b) It doesn’t interest me whether you succeed or not.　我对你成功与否不感兴趣。

　　c) It is in the morning that the murder took place.　谋杀案是在早上发生的。（强调句型）

　　d) It is John that broke the window.　是John打碎的窗户。（强调句型）

　　2. 用it 作形式主语的结构

　　(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 appears that…          似乎…

　　(4) It ＋ 过去分词 ＋ 从句

　　It is reported that…         据报道…

　　It has been proved that…     已证实…

　　It is said that…              据说…

　　3. 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。

　　（2）It is said /reported…结构中的主语从句不可提前。例如：

　　正确表达：It is said that President Jiang will visit our school next week.

　　错误表达：That President Jiang will visit our school next week is said.

　　（3）It happens/occurs…结构中的主语从句不可提前。例如：

　　正确表达：It occurred to him that he failed in the examination.

　　错误表达：That he failed in the examination occurred to him.

　　（4）It doesn’t matter how/whether …结构中的主语从句不可提前。例如：

　　正确表达：It doesn’t matter whether he is wrong or not.

　　错误表达：Whether he is wrong or not doesn’t matter.

　　（5）含主语从句的复合句是疑问句时，主语从句不可提前。例如：

　　正确表达：Is it likely that it will rain in the evening?

　　错误表达：Is that will rain in the evening likely?

　　4. what 与that 在引导主语从句时的区别

　　what 引导主语从句时在句时在从句中充当句子成分，如主语．宾语．表语，而that 则不然。例如：

　　a) What you said yesterday is right.

　　b) That she is still alive is a consolation