as可以作连词、介词及关系代词

as可以作连词、介词及关系代词。现将其用法小结如下:

一、as作连词的用法:

1. 作当……的时候,引导时间状语从句。注意与when、while的用法区别。

①when作当……的时候解,可以指较短的(一点)时间,也可指一段时间。如:

When he was at college, he could speak several foreign languages.

When the clock struck twelve, all the lights in the street went out.

②while常表示一段较长的时间或一个过程,强调主句谓语动词与从句谓语动词同时发生。如:

Work while you work. Play while you play.

③但属下列情形时,只用as, 而不用when或while。

A) 用于表示同一个人的两种动作交替进行,指一边……,一边……。如:

The girl dances as she sings on the stage.

He looked behind from time to time as he went forward.

B)表示两个同步发展的动作或行为,译为随着……。如:

As time went on / by, she became more and more worried.

As children get older, they become more and more interested in the things around them.

C)表示两个短促行为或事件几乎同时发生。如:

I thought of it just as you opened your mouth.

Just as the flying worm hit her face, she gave a loud cry.

D) 后接名词表示某一年龄段时,用as。如:

As a young man, he was active in sports.

2. as=since, 作既然、由于解,引导原因状语从句,常用来表示已为人们所知或显而易见的原因或理由。如: As / Since you're not feeling well, you may stay at home.

As he wasn't ready in time, we went without him.

3. as=in the way that, 作像、按照……的方式解,引导方式状语从句。如:

He speaks English as Americans do.

Remember, you must do everything as I do.

4. 用于as...as...或not so/ as...as...中,前一个as是副词,后一个as是连词,引导比较状语从句。如:

They helped the old man as often as possible.

I don't speak English so/ as well as he does.

5. 作虽然、尽管解,引导让步状语从句。常用倒装语序,即adj. /adv. / n.+as +主语+谓语+主句。如:

Tired as they were, they walked on.

Child as he is, he knows a lot. (child前不用冠词)

二、as作关系代词,引导定语从句,作正如、这一点解。如:

He is very careful, as his work shows.

As is well-known, Taiwan belongs to China.

as的这种用法,请看2001年的高考题:

is known to everybody, the moon travels round the earth once every month.

A. It

B. As

C. That

D. What

(字母下划横线的为正确答案)

另外,当先行词被the same, such等词修饰时,常用as来引导定语从句。如:

Such a clever boy as he can learn anything quickly.

I was reading the same book as he bought yesterday.