引导时间状语从句的从属连词
(1) 表示“当…时候”或“每当”的时间连词。主要的 when, while, as, whenever。如：
Don’t talk while you’re eating. 吃饭时不要说话。
Vegetables are best when they are fresh. 蔬菜新鲜时最好吃。
He came just as I was leaving. 我正要走时他来了。
(2) 表示“在…之前(或之后)”的时间连词。主要的有before, after。如：
Try to finish your work before you leave. 离开前设法把工作做完。
After we have finished tea, we will sit on the grass. 喝完茶之后我们将坐在草地上。
(3) 表示“自从”或“直到”的时间连词。主要的有since, until, till。如：
She’s been playing tennis since she was eight. 她从八岁起就打网球了。
Hold on until I fetch help. 坚持一下，等我找人来帮忙。
Never trouble trouble till trouble troubles you. (谚)不要无事惹事。(from )
(4) 表示“一…就”的时间连词。主要的有as soon as, the moment, the minute, the second, the instant, immediately, directly, instantly, once, no sooner…than, hardly…when等。如：
I’ll let you know as soon as I hear from her. 我一接她的信就通知你。
The moment I have finished I’ll give you a call. 我一干完就给你打电话。
I came immediately I heard the news. 我一听到这个消息，马上就来了。
Once you begin you must continue. 你一旦开始, 便不可停下来。
(5) 表示“上次”、“下次”、“每次”等的时间连词。主要的有every time(每次)，each time(每次)，(the) next time(下次)，any time(随时)，(the) last time(上次)，the first time(第一次)。如：
I’ll tell him about it (the) next time I see him. 我下一次见到他时，我就把这个情况告诉他。
We lose a few skin cells every time we wash our hands. 每当我们洗手的时候，我们都要损失一些皮肤细胞。
You can call me any time you want to. 你随时都可以给我打电话。
注意：every time, each time, any time前不用冠词，(the) next time, (the) last time中的冠词可以省略，而the first time中的冠词通常不能省略。