三大从句中的what,that和 which

三大从句中的what， that和 which
一．在名词性从句(主语从句、宾语从句、表语从句、同位语从句)中that 不充当任何句子成分，which 作定语，What 充当主语、宾语、表语等。

Eg:
It so happens that I know the man. (主语从句)
We have reason to believe that the fighting on the border may develop into a full-blown war.（宾语从句）
The trouble is that we are short of money.（表语从句）
The fact that she looked like a sensitive , kind girl didn’t matter.（同位语从句）
I don’t know which class he is in.
What he does doesn’t agree which what he says.
二．在定语从句中，what 不能引导定语从句，只需区分 that和which。

1.that 的先行词既可以是人，又可以是物，而which 的先行词只能是物。

2.当先行词是物时，that 和which经常可以互换。

Eg:
Do you still remember the days that/which we spent together?
Is this the museum that/which we visited last year?
3. 不可互换的情况：
用that 不用which有8种情况：
(1).当先行词被不定代词修饰或先行词本身是不定代词时。

不定代词有28个：
every/no/any/some (thing one body) much many (a) little/few all both none neither either each 。

Eg:
Is there anything that I can do for you?
All that is needed is a supply of oil.
(2)当先行词是序数词时或先行词被序数词 (the last, the next ) 修饰时。

Eg:
Our school is the first one that tries out this teaching method.
(3).当先行词是形容词最高级时或先行词被形容词最高级修饰时。

Eg:
This is the best film that I have seen.
(4).当先行词既有人又有物时。

The speaker will tell us about some writers and their works that are known to us.
He talked a lot about things and persons that they remembered in the school.
(5).主句是以which开头的特殊疑问句。

Which is the book that you brought me?
句子中有两个定语从句时，其中一个已用关系代词which , 另外一个宜用that ，Eg：
They secretly built up a small factory, which produced things that could cause pollution.
(6).当先行词由the only，the very, the right 等修饰时。

Eg:
This is t he very letter that I am looking for .
—Do you agree with her ideas at the meeting?
—Absolutely，what she's just said is the very idea that I want to express.
(7).当先行词在主句中作表语时，而关系代词在从句中作表语时。

Eg:
China is not the country that it used to be.
(8).当主句以here, there 开头且先行词是指物的名词时。

Eg:
There is no dictionary that you can find everything in.
用which不用that有三种情况：
(1).在非限制性定语从句中(指人时使用who或whom，指物时使用which)。

The river, which flows through London, is called the Thames.
We went to Mountain Tai last weekend，which，not surprisingly，was crowded with visitors.
(2). 介词前置时。

Eg:
He hasn’t got enough money with which he can buy the computer.
(3).当先行词本身是that时。

Eg：
That which is right speaks louder.
三．在状语从句中，what 和Which 均不能引导状语从句，that也只能引导九种状语从句中的两种，即目的状语从句和结果状语从句，也有说有表条件、原因和条件的。

Eg：
He is such a good teacher that the students love and respect him.（结果状语从句）He studied hard so that he could catch up with his classmates.（目的状语从句）Now that you've come, you'd better have dinner with us.（原因状语从句）
Seeing that he was a hard worker, he achieved a lot.（原因状语从句）
He was so excited that he couldn't fall asleep.(结果状语从句)
表示条件的：suppose/supposing (that), assume/assuming (that), provided/providing (that), given that等。

Suppose/ Supposing (that) we miss the train, what shall we do?
如果我们误了火车，我们将怎么办？
Assume that th eonly possible outcome is success,and then challenge yourself to prove how that can happen.
Assuming that neith er loses much more market share, both should start making an operating profit next year.
Given that he can get the same treatment again, he is sure to get well.。