(2)宜用which引导的定语从句

1) 当定语从句的介词提前时，要用which。

The house in which they lived last year has been rebuilt.

2) 引导非限制性定语从句时，要用which。

He bought a railway ticket for the woman, which helped her a lot.

1) 先行词与such, the same连用或先行词本身就是the same, such时，要用as。

Such people as you describe are rare nowadays.

Would you like to buy the same pen as I have?

2) 代替整个句子，在从句中作主语，而从句位于句首时，要用as。

As is well known, the earth goes around the sun.

当先行词是人称代词或是those, anyone等时，常用who。

Those who were either fools or unfit for their offices could not see the cloth.

（二）关系副词的用法：

1、when 指时间，在从句中作时间状语，它的先行词通常有：time, day, morning, night, week, year 等。如：

I still remember the time when I first became a college student.

Do you know the date when Lincoln was born?

注：when时常可以省略，特别是在某些句型和某些时间状语中。例如：

Each time he came, he did his best to help us.

But help never stopped coming from the day she fell ill.

2、where指地点，在从句中作地点状语。它的先行词通常有：place, spot, street, house, room, city, town, country等，如：