2. 表示“当…时候”的 while, when, as 的用法区别是：while从句中的谓语动词必须是延续性动词；表示带有规律性的“每当”或当主、从句谓语动词的动作发生有先后时，只能用 when；当表示“一边…一边…”或“随着”时，只能用 as。另外，用于此义的 as 所引导的时间状语从句谓语只能是动作动词，不能是状态动词。如下面一道高考题的答案是 B 而不能是A：
“I’m going to the post office.” “_____ you’re there, can you get me some stamps?”
A. As B. While C. Because D. If
3. until 在肯定句中通常只连用延续性动词，表示相应动作结束的时间；在否定句中通常连用非延续性动词，表示相应动作开始的时间，意为“直到…才”。如：
He waited until she was about to leave. 他等着一直到她准备离开。
I did not begin to work till he had gone. 他走了后我才开始工作。
4. 表示“一…就”除用 as soon as 外，还可用 the minute, the second, the instant, immediately, directly, instantly, no sooner…than, hardly…when 等。如：
I came immediately you called. 你一来电话我就来了。
Hardly had she arrived when it began to snow. 她刚到就下起雪来了。
The moment I have finished I'll give you a call. 我一干完就给你打电话。
5. every time, each time, (the) next time, (the) last time, by the time, the first time, any time 等以 time 结尾的词语也可用作连词，引导时间状语从句。如：
Next time you come in, please close the door. 下次你进来，请关门。
He didn’t tell me anything the last time I saw him. 上次我见到他时他什么也没告诉我。
By the time I got home, she had already gone to bed. 我到家时她已睡觉了。
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