as, when, while的區(qū)別：as, when, while都表示主、從句的動作或狀態(tài)同時發(fā)生，但三者意義不相同。

1. as和when引導(dǎo)的從句既可表示一點時間，也可表示一段時間，從句中的謂語動詞既可以是持續(xù)性動詞，也可以為短暫性動詞，經(jīng)?？梢曰Q使用;

His mother called him Robbie when he was a baby.

2. while引導(dǎo)的從句通常表示一段時間，從句中宜用持續(xù)性動詞作謂語。

I’ll look after the children while you are making dinner.

當從句中的謂語動詞為持續(xù)性動詞時，as, when, while可以通用，如：

Mother was worried because little Alice was ill, especially as / when / while father was away in France.媽媽擔(dān)心，因為小艾麗思病了，特別是當父親遠在法國的時候。

如果從句和主句要表示一個人的兩個動作交替進行或同時完成時，則多用as，可譯為“一邊......，一邊......”。

例如：

He looked behind from to time as he went.他一邊走，一邊不時地往后看。

As time goes on, it’s getting warmer and warmer..隨著時間的推移，天氣變得越來越暖了。

I thought of it just as you opened your mouth.你一張嘴我就知道你要說什么。(若表示兩個短促動作幾乎同時發(fā)生時，用as的場合多于when.)

當主從句之間表示轉(zhuǎn)折或?qū)Ρ汝P(guān)系時，多用while, 不用as或when。如：

She thought I was talking about her daughter, while in fact, I was talking about my daughter.她以為我在談?wù)撍畠?，而事實上，我在談?wù)撐业呐畠骸?/p>

如果表示從句的動作在主句的動作“之前”或“之后”發(fā)生時，多用when(=after), 不用as或 while。此外，when還含有“at that moment”的意思(= and then)，引起的句子不能放在句首，也不能用as, while來替換。例如：

He was about to leave when the telephone rang.他正要離開，忽然電話鈴響了。

We were watching TV when suddenly the lights went out.我們正在看電視，突然燈滅了。

They had just arrived home when it began to rain.他們剛到家，天就開始下雨了。