when与while的时态各有什么特点？

①when是at or during the time that, 既指时间点，也可指一段时间，while是during the time that，只指一段时间，因此when引导的时间状语从句中的动词可以是终止性动词，也可以是延续性动词，而while从句中的动词必须是延续性动词。

②when 说明从句的动作和主句的动作可以是同时，也可以是先后发生；while 则强调主句的动作在从句动作的发生的过程中或主从句两个动作同时发生。

③由when引导的时间状语从句，主句用过去进行时，从句应用一般过去时；如果从句和主句的动作同时发生，两句都用过去进行时的时候，多用while引导，如：

a. When the teacher came in, we were talking.

当此句改变主从句的位置时，则为：

While we were talking, the teacher came in.

b. They were singing while we were dancing.

④when和while 还可作并列连词。when表示“在那时”；while表示“而，却”，表对照关系。如：

a. The children were running to move the bag of rice when they heard the sound of a motor bike.

孩子们正要跑过去搬开那袋米，这时他们听到了摩托车的声音。

b. He is strong while his brother is weak.

他长得很结实，而他弟弟却很瘦弱。

when 一般突出“突然的”意思

while 一般指同时发生的事情 例如：

I was playing PC while he was looking TV

一般用现在时

when的使用范围很广，各种情景均可使用。

while强调两个动作同时进行。

while还可表转折，这点恰恰是试题中常见的。

给个例子：I was doing my homework,while he was watching TV in the sofa.

while作并列连词，意思是“而，却”，表对比

eg. He likes pop music,while I am fond of folk music.