when、as引導(dǎo)時(shí)間狀語從句時(shí)，側(cè)重點(diǎn)有所不同：when可指時(shí)間點(diǎn)，又可指時(shí)間段，從句中可用延續(xù)性動(dòng)詞，也可用非延續(xù)性動(dòng)詞。as多用于平行結(jié)構(gòu)，表示兩個(gè)動(dòng)作同時(shí)發(fā)生：一個(gè)主語同時(shí)進(jìn)行兩個(gè)動(dòng)作；一種狀態(tài)隨另一種狀態(tài)的變化而變化。表示主句的動(dòng)作發(fā)生在從句的較長動(dòng)作過程中，when、as均可使用。從句中為be動(dòng)詞時(shí)，多用when。

as,when和while的區(qū)別

1. As/When/While：A was happening, B happened或B happened as/when/while A was happening.

as,when,while用來表示“當(dāng)某事發(fā)生的時(shí)候，一個(gè)長的行為或事件正在進(jìn)行”。

當(dāng)從句引導(dǎo)的句子表示持續(xù)性動(dòng)作時(shí)，as/when/while引導(dǎo)的從句一般用過去進(jìn)行時(shí)（was/were+動(dòng)詞ing）。例如：

As I was walking down the street I saw Joe driving a Porsche.當(dāng)我正在沿著街道走的時(shí)候，我看到喬正開著保時(shí)捷。

The telephone rang when i was having a bath 當(dāng)我正在洗澡的時(shí)候，電話鈴響了。

as，when，while都可以用現(xiàn)在時(shí)態(tài)，如：

Please don't interrupt me when I'm speaking.當(dāng)我說話的時(shí)候，請(qǐng)不要打斷

I often get good ideas while I'm shaving.當(dāng)我刮胡子的時(shí)候，我經(jīng)常能想到好點(diǎn)子。

2. while A was happening,B was happening或While A happened, B happened

while用來表示兩個(gè)長動(dòng)作或事件過去同時(shí)發(fā)生，用過去進(jìn)行時(shí)或者過去時(shí)態(tài)。如：

While you were reading the paper ,I was working.當(dāng)你在讀報(bào)紙的時(shí)候，我正在工作。

John cooked supper while I watched TV.當(dāng)約翰在煮晚飯的時(shí)候，我在看電視。

也可以用現(xiàn)在時(shí)態(tài)，如：

After supper,I wash up while Mary puts the children to bed.晚飯后，當(dāng)瑪麗弄孩子們睡覺的時(shí)候我在洗漱。

3. As A happened,B happened.

B happened,as A happened.

as,when和while的區(qū)別

as 用在兩個(gè)短的行為或事件同時(shí)發(fā)生，如：

As I opened my eyes I heard a strange voice.當(dāng)我睜開眼睛的時(shí)候，我聽到奇怪的聲音。

The doorbell rang just as i picked up the phone.當(dāng)我拿起電話的時(shí)候，門鈴響了。