He decided to go to America，where he had a big company.

他决定到美国去，在那里他有一家大公司。

The little boy hid himself behind the door, from where he could see his mum enter the room.

那个小男孩躲在门后，从那里他可以看见他妈妈进入房间。

(2)一般情况下，where可以替换成"介词＋which"。

The school where/in which he teaches is not far from his home.

他教书的学校离他家不远。

We went back to the bus stop where/at which I had lost my wallet.

我们回到我丢失钱包的那个公共汽车站。

2．when

(1)when引导定语从句时，它的先行词是表示时间的名词(如：time，morning，day，month，year等)。when在定语从句中充当时间状语。有时when也可以和部分介词一起引导定语从句。

He was born in the year when the Second World War broke out.

他出生于二战爆发的那一年。

He came at the time when I didn't want to see him at all.

他在我根本不想见他的时候来了。

In the old days，when I was young，my hometown was very poor.

过去，在我小的时候，我的家乡很穷。

She went to Japan two years ago, since when I haven't heard from her.

她两年前去了日本，从那以后我没有收到过她的来信。

(2)when有时也可以用"介词＋which"代替。

The day when/on which I joined the Party is hard to forget.

我入党的那一天很难忘怀。

Do you still remember the year when/in which we met at a party for the first time?

你还记得我们第一次在晚会上相遇的那一年吗？

3．why

当先行词是reason时，用why引导定语从句。why在定语从句中作原因状语。

Do you know the reason why he was late?

你知道他迟到的原因吗？

4．如何确定用关系代词还是关系副词

解决这个问题的关键是看定语从句中缺少什么样的句子成分。如果缺少的是主语、表语或者宾语，就用关系代词；如果不缺少这些句子成分，缺少的是状语，就用关系副词。

二、"介词＋which/whom"结构

1．"介词＋which/whom"结构的用法

(1)"介词＋which"在定语从句中作时间、地点、原因状语，相当于关系副词when，where，why。