从句子结构上来说，句子有三种：简单句、并列句和复合句。简单句有一个主语或多个主语和一个谓语；一个主语和多个谓语。并列句是由并列连词连接的两个或多个简单句。复合句指的是含有两个或更多的主谓结构的句子，其中有一个（或更多）主谓结构充当句子的某一（些）成分，如主语、宾语、表语、定语、状语、同位语等。主语从句、宾语从句、表语从句、同位语从句、定语从句和状语从句都属于复合句。
一、状语从句：
状语从句 Adverbial Clause，从句用作状语称为状语从句。根据用途，状语从句可分为时间、地点、原因、条件、方式、让步、结果、目的等状语从句。
I. 时间状语从句
时间状语从句表示时间，常用的关联词有when, until, as, after, before, once, since, as long as, whenever等等。
例: 1) When you cross a main road, you must be careful.
2) He went out to play football after he had finished his homework.
3) Wait until you are called.
4) I can't recognize you. You are so changed since last we met.
5) He didn't go to school until he was eleven.
You can use my house as long as you are careful.
He is so terrible once he is drunk.
I listen to the radio while I walk every evening.
II. 地点状语从句
地点状语从句表示地点，常用的关联词有where, wherever, anywhere等。
例如：1) Put it where you found it.
2) Sit down wherever you like.
3) Anywhere she goes, he goes too.
III. 原因状语从句
原因状语从句表示原因或理由，常用的关联词有because, as, since, in case等。
1) I eat ice-cream so much because I like sweet food.
2) As I didn't know the way, I asked a policeman.
3) Since you won't help me, I'll ask someone else.
I'll take my raincoat in case it rains. (in case it rains = because it may rain)我将带上雨衣，以防下雨。
IV. 条件状语从句
条件状语从句表示真实的或现实的条件，引导从句所用的关联词有if, unless, suppose, in case(that), in the event (that), as (so) long as等等。
1) If it snows tomorrow, we will build a snowman.
You'll be late, unless you hurry.
3) Suppose we are late, what will he say? (suppose从句必须放在主句之前) 我们如果迟到了，他会说什么？
4) In the event that our team wins, there will be a party.
5) In case it rains, do not expect me. 如果下雨，就不要等我了。
6) He will do anything as(so) long as it is interesting. 只要好玩，他什么都愿意做。
V. 方式状语从句
方式状语从句表示动作的方式，回答How的问题，常用关联词as, as if, as though, the way(that), in the way(that)等引导，一般置于主语之后。
Do as I say. I did just as you told me. 照我说的去做。我就是照你说的去做的。
He acts as if/as though he is the owner. 他行为举止好象是这儿的主人似的。
They did it in a way that I had never seen before. 他们以我从没见过的方式行事。
I was never allowed to sing the way I wanted to. 我从未被允许用自己想用的方式唱歌。
VI. 让步状语从句
让步状语从句表示“虽然、尽管、即使”等概念，使句子具有对比的因素。常用的关联词有although, though, even if, even though, not that(=although…not)等，置于主语之前或后。
1) Although you feel very ill right now, this is still a common disease.
2) Though he has lived for years in London, he writes in French.
3) We intend to go U.S., even if air fares are expensive.
4) Even though fruits are good, you can't live with fruits only.
5) I'm OK now, not that I slept (although I did not sleep) very well last night.
VII. 结果状语从句
结果状语从句表示结果， 常由连词so…that, such(a/an)…that, so that, such that等引导，置于主语之后。
She was so frightened about the dog that she cried.
The news worried him so much that he didn't sleep at all for the whole night.
He is such a wonderful joker that you can't help laughing.
They are such wonderful players that no one can beat them.
We arrived early, so that we got good seats.
The weather was such that I couldn't go out.
VIII. 目的状语从句
目的状语从句表示目的，回答what for或 for what purpose的问题，常用关联词so that, in order that等引导，一般置于主语之后。目的状语从句中的谓语动词常由“情态动词+动词原形”构成。
Ships carry lifeboats so that people can escape if the ship sinks.
They wrote the notice in several languages so that foreigners could understand it.
We carved their names on the stone in order that people should always remember them.
They risk their lives so that/in order that they may support their kids.
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