在介詞后只能用which, 在口語中一般都把介詞放到從句后部去, 這時可以用that, 但省略的時候更多一些:

The tool with which he is working is called a wrench.

The tool (that) he is working with is called a wrench.

This is the question about which we've had so much discussion.

This is the question (that) we've had so much discussion about.

定語從句一般是修飾名詞或代詞的, 但間或也可以修飾整個句子a), 或是句子的一部分 b), 引導詞用which:

They have invited me to visit their country, which is very kind of them.

The activity was postponed, which was exactly what we wanted

When deeply absorbed in work, which he often was, he would forget all about eating and sleeping.

She was very patient towards the children, which her husband seldom was.

whose: 在表示“......的”這個概念時, 可用所有格 whose; whose 用于指物, 有時可與of which交替使用, 通常的詞序是 名詞詞組 + of which:

Is there anyone in your class whose family is in the northeast?

We had a meeting whose purpose was completely unclear. (…the purpose of which was…)

He's written a book the name of which I’ve completely forgotten. (…whose name I've…)

of which前的名詞詞組也可以由some, any, none, all, both, several, enough, many, most, few以及基數詞擔任; 這些詞也能用在 of whom之前.

The buses, most of which were already full, were surrounded by an angry crowd.

It's a family of eight children, all of whom are studying music.

關系副詞 when, where, why: 它們的含義相當于 at which, in which, for which, 因此它們之間有交替使用的可能.

The day when he was born…

on which he was born…

which he was born on…

The office where he works…

at which he works…

which he works at…

有時可用that替代關系副詞, 在口語中that 可省略.

Every time (that) the telephone rings, he gets nervous.

This was the first time I had serious trouble with my boss.

Do you know anywhere (that) I can get a drink?

This is the place (where) we met yesterday.

That is the reason (why) he did it.

在the way 后也可用that 替代in which, 在口語中that也可省略.

This is the way (that/in which) he did it.

That's the way I look at it.

如果定語從句中謂語為 there is, 作主語的關系代詞也常可省掉:

I must make full use of the time there is left to me and do as much as I can for the people.

This is the fastest train (that) there is to Nanjing.

定語從句的簡化: 定語從句與不定式結構, -ing分詞結構, -ed分詞結構以及無動詞分句等有著轉換關系.

He was the only one to realize the danger (= who realized the danger).

The woman driving the car (= who was driving the car) indicated that she was going to turn left.

The man injured by the bullet (= who was injured by the bullet) was taken to hospital.

All the women present (= who were present) looked up in alarm.