Ⅰ. as “當(dāng)(在)……時候”往往可與when 或while通用，但它著重指主句和從句的動作或事情相并發(fā)生。如：

① I saw him as he was getting off the bus. 當(dāng)下公共汽車的時候，我看見了他。

② As he walked on, he felt himself getting more and more tired.他繼續(xù)往前走的時候，感到越來越疲乏。

Ⅱ. when “當(dāng)(在)……的時候”主句和從句的動作或事情可以同時發(fā)生，也可以先后發(fā)生。

① It was raining when we arrived. 當(dāng)我們到達(dá)的時候，正下著雨。

② When we were at school, we went to the library every day. 我們在求學(xué)的時候，每天都到圖書館去。

Ⅲ. while “當(dāng)(在)……的時候”表主句的動作或事情發(fā)生在從句中的動作或事情的進(jìn)展過程之中。從句通常為進(jìn)行時態(tài)。它有時可與when通用，但它只能指一段時間(a period of time),而不能指一點(diǎn)時間(a point of time)如上面的第一個例子。又如：

① Please don’t talk so loud while others are working. 別人在工作的時候，請勿大聲講話。

② While I am washing the floor, you can be cleaning the windows.我洗地板時，你可以擦窗戶。

本文來自：逍遙右腦記憶 http://www.yy-art.cn/gaozhong/823678.html

相關(guān)閱讀：高一必修一英語Unit2單詞表