①when a. at the time that-clause指时间点，从句谓动短暂性动词 （有种“突然”的含义） b．during the that-clause指一段时间，谓动延续性动词。 ②while during the time that只指一段时间，谓动必须是延续性动词。（相当于when的第二种。）
如：i. I was doing my homework when the baby cried.(时间点，短暂性动词) ii．When/while I worked in Beijing, I met a lot of foreigners.（时间段，延续性动词）
iii．We were talking when the teacher came in iv．When/while we were talking, the teacher came in. （主句从句动作） When a． 同时发生 b． 先后发生 如When I worked in Beijing, I made a lot of friends.（同时发生）当我在北京工作的时候我交了很多朋友。 When I arrived at the cinema, the film was over. (先后发生)当我当电影院的时候，电影已经结束了。
While 在 从句动作 的发生的过程中 b．同时发生。 如： The teacher came in while we were talking。（came in在were talking发生的过程中） They were singing while we were dancing.（同时发生）
，主句用过去进行时，when从句应用一般过去时； ，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/when we were talking, the teacher came in. b. They were singing while we were dancing.
B作并列连词的区别 a．when “在那时” “突然” b．while “而，却”，表对照关系，轻微的转折。 如： a. We were doing our homework when the light went out.（我们正在做家庭作业，就在那时灯熄灭了。） b. He is strong while his brother is weak. 他长得很结实，而他弟弟却很瘦弱。 He likes English while he likes math. ，while，as 引导时间状语从句的区别 when，while，as显然都可以引导时间状语从句，但用法区
