As 的托福考点总结

1. 作从属连词引导时间状语从句，表示“当”、“一边……一边”。

I pulled a muscle as I was lifting a heavy suitcase.

Parts are replaced as they grow old.  

注意：as不能用来表示在某一时间，如 As I started work here, the pay was $4 an hour. (x) 而应说When I started work here, the pay was $4 an hour.

2. 作从属连词引导原因状语从句，表示“因为”，等同because, since。

As the gorilla is so big and powerful, it has no real enemies.

As 常用于句首，但是当表达某件事的某一特殊原因时，在as前面可以用especially或particularly，此时as 引导的原因状语从句放在主句后面，如 I was frightened when I went to bed, especially as my room was so far up.

3. 作从属连词引导方式状语从句，置于主语之后，表示“按照”、“根据”。

Type this again as I showed you a moment ago.

4. 作从属连词引导比较状语从句，表示“像……一样”。

He looked over his shoulder as Jack had done.

5. 作副词，用于形容词前，表示“被认为”。

They regarded manual work as degrading.

6. 作介词，表示“以……身份”、“作为”、“当作”。

He is greatly respected both as a person and as a politician.

7. 作介词，表示“像”。

The bread is as hard as a brick.

注意：通常在将一件事或人同另一件事或人进行比较时，名词词组前不用as而用like.

He swims like a fish.

Children, like animals, are noisy at meal times.