状语从句的用法
在句中作状语的从句称为状语从句。状语从句在句中的位置比较灵活，可以放在主句之前或之后，偶尔也可插在主句之中。状语从句由从属连词引导，不同的连词引出不同的状语从句。状语从句一般可分为九大类，分别表示时间、地点、条件、原因、结果、目的、方式、比较和让步。
1.时间状语从句
1)引导时间状语从句的从属连词很多，常见的有before, after, when, while, as, since, till, until, as soon as等。
She began to watch TV after she had finished her homework.
她做完作业后，才开始看电视。
Be a pupil before you become a teacher.
先做学生，再做先生。
2)表示“当……时候”的when, while和as的用法区别是：when既可以指某一点时间也可以指某一段时间，其谓语动词可以是延续性的，也可以是非延续性的；while只能用来表示某一段时间，不能用来表示某一点时间，其谓语动词只能是延续性的；as常用来引导两个动作紧接着发生，强调“同一时间”或“一先一后”，可以翻译成“边……边……”。
When the teacher came in, we were talking and laughing.
当老师进来时，我们正在有说有笑。
While we were talking, the bell rang.
我们在谈话时，铃响了。
The students took notes as they listened.
学生们边听边做笔记。
3)表示“一……就”，除用as soon as外，还可用the moment, the minute, the second, the instant, directly, instantly, immediately, no sooner…than, hardly…when等。
I will tell him the good news as soon as he comes back.
他一回来我就会告诉他这个好消息。
The moment you hear the news, give me a call.
你一听到消息就给我打电话。
Immediately he came home, I told him about it.
他一回到家，我就告诉他这件事。
Hardly had she arrived when it began to snow.
她刚到就下起雪来。
4)every time, each time, the first time, (the) next time, (the) last time, any time, by the time等以time结尾的词语也可用来引导时间状语从句。
Every time she came to the city, she would visit her old friends.
她每次来到城里都要去看看她那些老朋友。
You can call me any time you want to.
你可以随时给我打电话。
The last time I went to Beijing, I visited many places.
我上次到北京时曾游览过许多地方。
By the time I got there, he has already gone.
我到那时他已经走了。
5)until和till意思一样。till在口语中用得较多，until多用在正式文体中，但在句首只能用until。在肯定句中谓语为延续性动词时表示“直到……为止”，在否定句中谓语为终止性动词时表示“直到……才”。
I’ll wait until/till he came back.
我将一直等到他回来。
I did not begin to work until he had gone.
他走了后我才开始工作。
2.地点状语从句
引导地点状语从句的从属连词主要有where, wherever, everywhere, anywhere。
You should put the book where it was.
你应该把书放在原来的地方。
Wherever I am, I will be thinking of you.
无论我在哪里，我都会想着你。
Everywhere they went, they were kindly received.
他们所到之处，都受到热情款待。
He will meet you anywhere you want.
他随你在哪儿见面都行。
3.条件状语从句
引导条件状语从句的从属连词主要有if, unless, as/so long as, in case, if only, on condition that, suppose (that)/supposing (that), provided (that)/providing (that)等。
If you study hard, you will pass the examination.
如果你努力学习，你就会通过考试。
Unless it rains, he usually goes to school on foot.
除非天下雨，他通常是走路去上学。
As long as you need me, I’ll stay.
只要你需要我，我就留下来。
In case I forget, please remind me of it.
如果我忘了，请提醒我。
I’ll come on condition that Robert is invited too.
如果罗伯特也受到邀请，我就来。
Suppose (that) you had one million dollars, what would you do?
假如你有一百万美金，你会怎么办？（可用于虚拟语气）
Supposing (that) this is not the right way to the station, what shall we do?
假如这不是去车站的路，我们该怎么办？（不用于虚拟语气）
4.原因状语从句
引导原因状语从句的从属连词主要有because, as, for, since, seeing that, now that, considering that, in that等。
I can’t get there on time because I’m lost.
因为迷路，我不能按时到达。
As it is raining, let’s stay at home.
因为下雨，我们就留在家里吧。
It must have rained last night, for the ground is wet this morning.
昨夜一定下雨了，今天早上地都是湿的。
Since you are going, I will go.
既然你去，我也去。
Seeing (that) he is ill, he is unlikely to come.
他生病了，不可能会来。
Now (that) you are ready, we’ll start working at once.
既然你们准备好了，我们马上开始工作。
5.结果状语从句
引导结果状语从句的从属连词主要有so...that, such (a)...that, so, so that等。
He runs so fast that I couldn’t follow him.
他跑得太快，我跟不上。
She gave us such an excellent lecture that we’ll never forget.
她给我们做了一次非常精彩的演讲，我们永远都不会忘记。
He was late again, so the teacher was very angry.
他又一次迟到了，所以老师很生气。
You went early, so that you finished your work on time.
你们去得早，因此按时完成了工作。
6.目的状语从句
引导目的状语从句的从属连词主要有so that, in order that, lest, for fear, in case等。
We left early so that we could catch the first train.
我们很早出发，以便能赶上第一班火车。
He works hard in order that he can pass the exam.
他努力学习，以便能够通过考试。
He ran away lest he (should) be caught.
他怕被抓，因而逃走了。
He ran away for fear that he should be seen.
唯恐被人发现，他逃离了。
Take a taxi in case you are late for the meeting.
坐出租车去，免得开会迟到。
7.方式状语从句
引导方式状语从句的从属连词主要有as, just as(…so), as if/as though。
Air is to man as water is to fish.
空气之于人，犹水之于鱼。
You should do (just) as I tell you.
你要照我说的去做。
He speaks English as if/as though he were an Englishman.
他说起英语来好像是英国人一样。
8.比较状语从句
引导比较状语从句的从属连词主要有the+比较级…the+比较级, than, as…as, not so/as…as。
The more you exercise, the healthier you will be.
你越加锻炼，就会越加健康。
This book is more difficult than we thought.
这本书比我们想的要难。
This film is as interesting as that one.
这部电影和那部一样有趣。
It is not so/as easy as you think.
它没有你想的那么容易。
9.让步状语从句
引导让步从句的从属连词主要有though, although, as, even if, even though, 疑问词+ever, no matter+疑问词，whether…or等。
We were not tired though/although we had worked all day.
虽然我们干了一天活，但并不累。
Even if/though I fail, I’ll keep on trying.
即使我失败了，我会继续努力。
Teacher as he is, he can’t know everything.
虽然是老师，他也不可能什么都懂。
Whoever you are, you should obey the rules.
不管你是谁，你都应该遵守规定。
Whether his suggestion is right or not, we want to have a try.
不管他的提议是否正确，我们还是想试一试。