3. 如何区分as, when, while
I kept silent ______ he was speaking.
A. as B. when C. while D. that
此题应选C。关于as, when, while 表示“当……的时候”的区别, 可作如下归纳：
1. 若主句表示的是一个短暂性动作, 而从句表示的是一个持续性动作, 则三者均可用：
He fell asleep when [while, as] he was reading. 他看书时睡着了。
2. 若主从句表示两个同时进行的持续性动作, 且强调主句表示的动作延续到从句所指的整个时间, 一般只用while：
While he played the piano, I cooked the dinner. 他弹钢琴时, 我做了饭。
3. 若主从句动作同时发生, 且强调“一边……一边”这样的意思, 一般要用as：
She sang as she went along. 她边走边唱。
4. 若从句是一个短暂性动作, 而主句是一个持续性动作, 可用 as / when, 但不能用 while：
When [As] he came, I was listening to the radio.
他来时, 我在听收音机。
5. 若主从句表示的是两个同时发生的短暂性动作, 一般用as(也可用when)：
I thought of it just as [when] you opened yourmouth. 就在你要说话的时候, 我也想到了。
6. 表示“每当……的时候”(强调规律性);或主从句动作不是同时发生, 而是有先后顺序, 一般都用when：
It’s cold when it snows. 下雪时天冷。
I’ll go when he comes back. 他回来时, 我就走。
4. 关于hardly...when及no soooner...than
He had hardly arrived at the station ______ the train began to leave.
A. when B. that C. than D. where
此题要选A。容易误选C。以下两类句型意思和用法大致相同, 但搭配不同：
a. hardly...when...
b. no sooner...than...
以上句型需注意以下几点：
(1) 两个句型均指“一……就……”, 句型a中的hardly也可换成scarcely, barely；其中的when也可换成before。但是, 千万不要将句型a中的when与句型b中的than弄混。
(2) 以上两类句型的主句通常是过去完成时, 而从句通常应是一般过去时。
(3) 若将hardly, no sooner置于句首, 其后要倒装句式。
1. I had hardly closed my eyes ____ the telephonerang.
A. when B. that C. than D. where
2. Hardly had we arrived ____ it started to rain.
A. when B. that C. than D. where
3. He had no sooner heard the knock ____he opened
the door.
A. when B. that C. than D. where
4. No sooner had he done it _____ he knew he hadmade a mistake.
A. when B. that C. than D. where
答案：1. A 2. A 3. C 4. C