as可以作連詞、介詞及關(guān)系代詞。在英語四級(jí)考試中經(jīng)常會(huì)用到，現(xiàn)在，小編現(xiàn)將其用法小結(jié)如下，大家可以作為參考。

一、 as作連詞的用法:

1. 作"當(dāng)……的時(shí)候",引導(dǎo)時(shí)間狀語從句。注意與when、 while的用法區(qū)別。

① when作"當(dāng)……的時(shí)候"解,可以指較短的(一點(diǎn))時(shí)間,也可指一段時(shí)間。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.

② while常表示一段較長的時(shí)間或一個(gè)過程,強(qiáng)調(diào)主句謂語動(dòng)詞與從句謂語動(dòng)詞同時(shí)發(fā)生。如:

Work while you work. Play while you play.

③ 但屬下列情形時(shí),只用as, 而不用when或while。

A) 用于表示同一個(gè)人的兩種動(dòng)作交替進(jìn)行,指"一邊……,一邊……"。如:

The girl dances as she sings on the stage.

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

B)表示兩個(gè)同步發(fā)展的動(dòng)作或行為,譯為"隨著……"。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)表示兩個(gè)短促行為或事件幾乎同時(shí)發(fā)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) 后接名詞表示某一年齡段時(shí),用as。如:

As a young man, he was active in sports.

2. as=since, 作"既然"、"由于"解,引導(dǎo)原因狀語從句,常用來表示已為人們所知或顯而易見的原因或理由。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,引導(dǎo)方式狀語從句。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,前一個(gè)as是副詞,后一個(gè)as是連詞,引導(dǎo)比較狀語從句。如:

They helped the old man as often as possible.

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

5. 作"雖然"、"盡管"解,引導(dǎo)讓步狀語從句。常用倒裝語序,即adj. /adv. / n.+as +主語+謂語+主句。如:

Tired as they were, they walked on.

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

以上就是內(nèi)容就是關(guān)于英語四級(jí)語法知識(shí)，希望可以給大家在備考的時(shí)候帶來幫助。