1.當先行詞為all, little, much, few, everything, none 等不定代詞時關系代詞用that而不用which.

I will tell him all that you told me at the ball.

There are few books that you can read in this book store.

2.當先行詞既有人又有物時,關系代詞用that, 不用which.

He asked about the factories and workers that he had visited.

3.當先行詞有形容詞最高級修飾時,關系代詞用that, 而不用which.

This is the best novel that I have ever read.

Guilin is one of the most beautiful cities that I have ever visited.

4.當先行詞有序數詞修飾時,關系代詞用that, 不用which.

The first sight that was caught at the Great Wall has made a lasting impression on him.

5.當先行詞被the only, the very, the same, the right等修飾時,關系代詞用that,不用which.

That is the very thing that we can do.

It is the only book that he bought himself.

6.當先行詞被all, every, any, much, little, few, no等修飾時,關系代詞用that,不用which.

You can take any room that you like.

There is no clothes that fit you here.

7.當主句是以which開頭的特殊問句時,定語從句關系代詞一般用that而不用which.

Which of the books that had pictures was worth reading?

8.在強調句型" It is ... that ..." 中,只用that,不用which.

It is in this room that he was born twenty years ago.

9.在" such (the same) ... as ..." 句型中,關系代詞要用as, 而不用which.

We need such materials as (not which) can bear high temperature.

10.表示" 正如... 那樣 "," 正象..." 之意時, 用as, 不用which.

Mary was late again, as had been expected.

11.As 引導的定語從句可以放在主句前面, 也可以放在主句后面或主句中間,而由 which引導的定語從句只能放在主句后面。

As we all know, oceans cover more than 70% of the earth