本试题 “_____ she couldn't understand was _____ fewer and fewer students showed interest in her lessons.[ ]A. What; whyB. That; whatC. What; becauseD. Why;...” 主要考查您对主语从句
表语从句
等考点的理解。关于这些考点您可以点击下面的选项卡查看详细档案。
主语从句的概念：
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。主语从句通常由从属连词that，whether，if和连接代词what，who，whichwhatever，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。
主语从句用法：
1、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：
如：That he is still alive is a wonder. 他还活着，真是奇迹。
When we arrive doesn't matter. 什么时候到没有关系。
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。
Whether they would support us was a problem. 他们是否会支持我们还是一个问题。
2、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：
如：It's a pity that he didn't come. 很遗憾他没来。
(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句：
如：Whether they would support us was a problem. 他们是否会支持我们还是一个问题。
It was a problem whether they would support us. 他们是否会支持我们还是一个问题。
(3)对关系代词型what引导的主语从句，通常不用形式主语，总是主语从句放在句首：
如：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。
(4)如果句子是疑问句，则必须用带形式主语it的结构：
如：Is it true that he is the girl's father? 他是那女孩的父亲，是真的吗？
How is it that you are late again? 你怎么又迟到了？
3、连词that的省略问题：
引导主语从句的连词that有时可省，有时不能省，其原则是：
若that引导的主语从句直接位于句首，则that不能省略；
若that引导的主语从句位于句末，而在句首使用了形式主语it，则that则可以省略：
如：That you didn't go to the talk was a pity. 很遗憾你没去听报告。(that不可省)
It was a pity(that) you didn't go to the talk. 很遗憾你没去听报告。(that可省)
主语从句应注意的几个问题：
1、that引导的主语从句既可放在句首，也可放在句尾，但在下列情况下that从句不可提前。
（1）在It is said/reported...that结构中：
如：It is reported that a bank was robbed yesterday.
（2）在Ithappened/occurred...结构中：
Ithappenedthattheteacherwasnotintheofficethatday.
（3）含主语从句的复合句是疑问句时：
如：Is it ture that you will give up the job?
2、下面这种情况常用it作形式主语。在It doesn't matter+what/whatever…结构中。
如：It doesn't matter what you say.
3、由what引导的主语从句谓语动词单复数问题 what引导的主语从句一般按单数对待，但是，在实际使用中究竟按单数还是按复数对取决于其成分的含义。
如：What we need is more time.
What were left behind were five empty bottles.
表语从句的概念：
用作表语的从句叫作表语从句，它位于主句中的连系动词之后。引导表语从句的词有
从属连词that、whether、as though(if)；
关系代词who, what, which, whom, whose, whatever, whoever, whomever, whichever等；
关系副词when, where, why, how, however, when。
表语从句用法：
1、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：
如：The fact is that he doesn't really try. 事实是他没有做真正的努力。
The question is whether the film is worth seeing. 问题是这部电影是否值得看。
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。
It isn't as if you were going away for ever. 又不是你离开不回来了。
It is because I love you too much. 那是因为我太爱你了。
注：whether可此导表语从句，但与之同义的if 却通常不用于引导表语从句；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。
2、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：
如：My idea is(that) we should do it right away. 我的意见是我们应该马上干。
The trouble is(that) he is ill. 糟糕的
表语从句用法拓展：
名词性从句在be等系动词后作表语时被称为表语从句，表语从句只能置于主句之后，而主句的动词只能是联系动词。
例如：The problem is how we can get the things we need. 问题是我们怎样能弄到我们需要的东西。(how在表语从句中充当方式状语)
The scissors are not what I need. 这把剪刀不是我所需要的。(what在表语从句中充当宾语)
What I told him was that I would find him a good play.
我告诉他的是我会给他找个好剧本。(what在主语从句中作直接宾语，that作为表语从句的引导词在该表语从句中不充当句子成分，不能省略)
That is what I want to tell you. 那就是我想要对你讲的。(what在表语从句中充当直接宾语)
That is why she failed to pass the exam. 那就是她考试不及格的原因。(why在表语从句中充当原因状语)
注意：“That is why...”是常用句型，意为“这就是……的原因/因此……”，其中why引导的名词性从句在句中作表语，该句型通常用于针对前面已经说明过的原因进行总结：
如：That is why you see this old woman before you know, Jeanne.珍妮，这就是现在这个老太婆出现在你面前的原因。(前文提到Jeanne对老妇人显得苍老憔悴深感诧异，说话人对她讲述了其中的原因之后，用这一句来进行概括)。//ThatiswhyIcame.这就是我来的原因。下面是两个与“That is why...”形式相似的结构，它们与“That is why...”结构之间的关系要能够辨析清楚：
（1）“That is why...”与“That is the reason why...”同义，只不过从语法结构上讲，“That is the reason why...”中why引导的是—个定语从句，将其中的the reason去掉则与“That is why...”结构一样：
如：That is(the reason) why I can not agree. 这就是我不能同意的理由。
（2）“That is because...”句型中从属连词because引导的名词性从句在此作表语，这也是个常用句型，意为“这就是为什么……/因为……”。“That is because...”与“That is why...”之间的不同在于“That is because...”指原因或理由，“That is why...”则指由于各种原因所造成的后果：
如：He did not see the film last night.
That is because he had to help his little sister with her homework. 昨天晚上他没有去看电影，那是因为他得帮助他的妹妹做作业。(第一句话说明结果，第二句话说明原因)
He had seen the film before. That is why he did not see it last night. 他以前曾看过那部电影，因此他昨天晚上没有去看。(第一句话说明原因，第二句话说明结果)
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