1. when可以指代时间点或时间段,适用于终止性动词和持续性动词。例如:
- When I got home, he was having supper.(我到家时,他正在吃饭。)
- When I was young, I liked dancing.(我年轻时喜欢跳舞。)
2. while仅指时间段,适用于持续性动词。例如:
- While I slept, a thief broke in.(在我睡觉时,一个盗贼闯了进来。)
3. when从句与主句动作先后发生时,不能与while互换。例如:
- When he has finished his work, he takes a short rest.(每当他做完工作后,总要稍稍休息一下。)
- When I got to the cinema, the film had already begun.(当我到电影院时,电影已经开始了。)
4. when从句动词为终止性动词时,不能由while替换。例如:
- When he came yesterday, we were playing basketball.(昨天他来时,我们正在打篮球。)
5. 当从句的谓语是表动作的延续性动词时,when, while才有可能互相替代。例如:
- While / When we were still laughing, the teacher came in.(正当我们仍然大声嬉笑时,老师进来了。)
6. 当从句的谓语动词是终止性动词,而且主句的谓语动词也是终止性动词时,when可和as通用,用as比用when在时间上更为紧凑,有"正当这时"的含义。例如:
- He came just as (or when) I reached the door.(我刚到门那儿,他就来了。)
7. 从句的谓语动词如表示状态时,通常用while。例如:
- We must strike while the iron is hot.(我们应该趁热打铁。)
8. while和when都可以用作并列连词。例如:
- Mike is tall while his brother is short.(迈克的个子很高,然而他弟弟很矮。)
- Mary was on her way home when two big boys stopped her.(玛丽正走在回家的路上,这时两个大个子男孩拦住她。)
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