时间状语从句
时间状语从句就是在复合句中表示主句动作发生时间的状语从句。
1. 用when引导：when表示“当……时候”。
Things were different when I was a child.
2. 用while引导：while表示“当……时候”。
I went swimming while the others played tennis.
While my mother is cooking, my father is reading newspaper.
I was shocked when the little baby fell from its bed.
注意：while 所引导的时间状语从句中谓语动词必须是持续性的，不能是短暂性的。
3. 用as引导：as表示“当……时候”“随着”。如：
We get wiser as we get old.
随着生产工艺的改进(the process of production/ update)，工厂的生产效率(productivity)也大大地提高了。
The factory’s productivity improves remarkably as the process of production is updated.
随着积累的经验越来越多(accumulate experience)，这群年轻人能够更熟练地解决问题。(sophisticatedly adv.)
These young can solve problems more sophisticatedly as more and more experience is accumulated.
4. 用before引导：before表示“在……之前”。如：
Turn off the lights before you go to bed.
5. 用after引导：after表示“在……之后”。
I will tell you after they leave.
6. 用until / till引导：until / till表示“直到……”。如：
I watched him until he disappeared in the distance.
She didn’t marry until she was over fifty.
7. 用since引导：since表示“自从……以来”。
We have known each other since we were children. 我们从小认识。
8. 用as soon as引导：as soon as表示“一……就……”。
He started as soon as he received the news.
表示“一……就……”这一意思的连词，除as soon as外，还可用the moment, the minute, the instant等。如：short-term instant interest 即时利益 instant effect
The moment I saw him I knew there was no hope.
原因状语从句
原因状语从句就是在复合句中表示主句动作发生原因的状语从句。
1. 用because引导：because是引导原因状语从句最常用的连词，其意为“因为”。
I bought the house simply because it was large.
2. 用as引导：as也可以用于引导原因状语从句，意思是“由于”。
As he is ill, he can’t come to the meeting. 由于生病了，他不能来参加会议。
3. 用since引导：since引导原因状语从句时，意思是“既然”。
Since you ask, I will tell you.
4. 用now that引导：now that引导原因状语从句的意思也是“既然”。如：
Now that you’re growing up, you must learn to stand on your own two feet.
