1. while 引导的时间状语从句既可放在句首,也可放在句末;而 while 引导的让步状语从句一般放在句首,不放在句末。另外,也可以从意义上加以区分。例如:
While he was tired, he went on working.
(虽然他累了,但他还是继续工作。)
( while 引导让步状语从句)
While he was tired, he would have a rest.
(他累了就休息一会儿。)
( while 引导时间状语从句)
2. while 引导让步状语从句时,如果从句的主语和主句的主语相同,那么从句的主语和谓语动词 be 都可以省略。例如:
While he was ill, he went there. (= While ill, he went there.)
(虽然他有病,但他还是去那里了。)
3. while 和 when 都可以引导时间状语从句,但应注意: while 引导的时间状语从句中的谓语动词必须是延续性的动词;而 when 引导的时间状语从句中的`谓语动词既可以是延续性动词,也可以是非延续性动词。当时间状语从句中的谓语动词是延续性动词时, while 和 when 可以互相替换。例如:
While we were talking, the teacher came in.
(我们正在谈话时,老师进来了。)
The bus had left when we arrived at the bus stop.
(当我们到达车站时,公共汽车已经开走了。)
( arrive 是非延续性动词,因此,此句中的 when 不能用 while 替换。)
When / While we were having a meeting, our teacher came in.
(我们正在开会时,老师走了进来。)
( have 是延续性动词,因此,句中的 when 可以用 while 替换。)
4. while 引导的状语从句还可以表示“某个动作正在进行的同时,另一个动作也在进行之中”。例如:
While the teacher was speaking, the students were listening.