英语三大从句
1名词性从句：主从，宾从，表从，同从
2定从（adj）
3状从（adv）
A：名词性从句
I主从：
为句子平衡，通常在主从用形式主语it，将真正的主语从句移至句末
(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 amazing that she should have said nothing about it. 她竟未谈及此事令人惊讶。
(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：
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，通常直接将主语从句放在句首。如：
What we need is money. 我们需要的是钱。
(4) 如果句子是疑问句，则必须用带形式主语it的结构：
How is it that you are late again? 你怎么又迟到了？
三、连词that的省略问题
若that引导的主从位于句首，则that不能省；
若that引导的主从位于句末，在句首有it，that可省：
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)
II宾从：
一、引导词
（1）that 引导，动词如say, think, wish , hope, see, believe, a*, expect, hear , feel后，conj-that只起连接作用，不做句子成分。
如：I told him that he was wrong.
Note:
在think, believe, suppose, expect等动词引起的宾语从句中，将think 等动词变为否定形式。
如：I don’t think you are right.
（2）if、 whether
一般情况下，whether和if 可以替换。
Note:
1在介词后面的宾语从句中不用if引导
2宾语从句中有or not时不用if引导
3和不定式连用作宾语时不用if引导
Whether to go there or not hasn’t been decided.
（3）连接代词who, whom, whose, what, which和连接副词when, where, why, how 等连接的宾语从句，就是WH开头的，它们在句中即有连接从句的作用，又在句中充当句子的成分。
二、宾语从句的语序，
宾语从句的语序必须是陈述语序，既连接词+主语+谓语+其他成分
Note：
有问句作为从句出现不改变语序。
What's the matter? What's wrong? What's up？
三、宾语从句的时态。
1) She says that she is a student.→ She said that she was a student.
2) She says that she will fly to Japan in a week. → She said that she would fly to Japan in a week.
3) She says that she has finished her homework already. → She said that she had finished her homework already.
（1）如果宾语从句说的是客观真理、自然现象或事实时，这时宾语从句要用一般现在时态。
（2）Could you tell me…是用来征询对方的意见，委婉，不表示过去。
