英语：什么是复合句?

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.
二、定语从句

定语从句（Attributive Clauses）在句中做定语,修饰一个名词或代词,被修饰的名词,词组或代词即先行词.定语从句通常出现在先行词之后,由关系词（关系代词或关系副词）引出.

关系代词有：who, whom, whose, that, which等.
关系副词有：when, where, why等

1. 关系代词引导的定语从句

关系代词所代替的先行词是人或物的名词或代词,并在句中充当主语、宾语、定语等成分.关系代词在定语从句中作主语时,从句谓语动词的人称和数要和先行词保持一致.

1）who, whom, that 这些词代替的先行词是人的名词或代词,在从句中所起作用如下：
Is he the man who/that wants to see you?
他就是你想见的人吗?（who/that在从句中作主语）
He is the man whom/ that I saw yesterday.
他就是我昨天见的那个人.（whom/that在从句中作宾语）

2) Whose 用来指人或物,(只用作定语, 若指物,它还可以同of which互换）,例如：
They rushed over to help the man whose car had broken down.
那人车坏了,大家都跑过去帮忙.
Please pass me the book whose (of which) cover is green.
请递给我那本绿皮的书.

3） which, that 它们所代替的先行词是事物的名词或代词,在从句中可作主语、宾语等,例如： A prosperity which / that had never been seen before appears in the countryside.
农村出现了前所未有的繁荣.（which / that在句中作宾语）
The package (which / that) you are carrying is about to come unwrapped.
你拿的包快散了.(which / that在句中作宾语)

2. 关系副词引导的定语从句

关系副词可代替的先行词是时间、地点或理由的名词,在从句中作状语.
1）when, where, why 关系副词when, where, why的含义相当于"介词+ which"结构,因此常常和"介词+ which"结构交替使用.例如：
There are occasions when (on which) one must yield. 任何人都有不得不屈服的时候. Beijing is the place where (in which) I was born. 北京是我的出生地.
Is this the reason why (for which) he refused our offer?
这就是他拒绝我们帮助他的理由吗?

2）that代替关系副词that可以用于表示时间、地点、方式、理由的名词后取代when, where, why和"介词+ which"引导的定语从句,在口语中that常被省略.例如：
His father died the year (that / when / in which) he was born.
他父亲在他出生那年逝世了.
He is unlikely to find the place (that / where / in which) he lived forty years ago.
他不大可能找到他四十年前居住过的地方

3. 判断关系代词与关系副词
方法一： 用关系代词,还是关系副词完全取决于从句中的谓语动词.及物动词后面无宾语,就必须要求用关系代词；而不及物动词则要求用关系副词.例如：
This is the mountain village where I stayed last year.
I'll never forget the days when I worked together with you.

习惯上总把表地点或时间的名词与关系副词 where, when联系在一起.

方法二： 准确判断先行词在定语从句中的成分(主、谓、宾、定、状),也能正确选择出关系代词/关系副词.
4. 限制性和非限制性定语从句
1) 定语从句有限制性和非限制性两种.限制性定语从句是先行词不可缺少的部分,去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明,去掉了也不会影响主句的意思,它与主句之间通常用逗号分开,例如：
This is the house which we bought last month.
这是我们上个月买的那幢房子.（限制性）
The house, which we bought last month, is very nice.
这幢房子很漂亮,是我们上个月买的.（非限制性）

2) 当先行词是专有名词或物主代词和指示代词所修饰时,其后的定语从句通常是非限制性的,例如： Charles Smith, who was my former teacher, retired last year.
查理·史密斯去年退休了,他曾经是我的老师.
My house, which I bought last year, has got a lovely garden.
我去年买的的那幢房子带着个漂亮的花园.
This novel, which I have read three times, is very touching.
这本小说很动人,我已经读了三遍.

3) 非限制性定语从句还能将整个主句作为先行词, 对其进行修饰, 这时从句谓语动词要用第三人称单数,例如：
He seems not to have grasped what I meant, which greatly upsets me.
他似乎没抓住我的意思,这使我心烦.
Liquid water changes to vapor, which is called evaporation.
液态水变为蒸汽,这就叫做蒸发.

说明：关系代词that和关系副词why不能引导非限制性定语从句.

5. 介词+关系词
1）介词后面的关系词不能省略.
2）that前不能有介词.
3） 某些在从句中充当时间,地点或原因状语的"介词+关系词"结构可以同关系副词when 和where 互换.
This is the house in which I lived two years ago.
This is the house where I lived two years ago.
Do you remember the day on which you joined our club?
Do you remember the day when you joined our club?

6. as, which 非限定性定语从句
由as, which 引导的非限定性定语从句,as和which可代整个主句,相当于and this或and that.As一般放在句首,which在句中.
as 和which在引导非限制性定语从句时,这两个关系代词都指主句所表达的整个意思,且在定语从句中都可以作主语和宾语.但不同之处主要有两点：
(1） as 引导的定语从句可置于句首,而which不可.
(2） as 代表前面的整个主句并在从句中作主语时,从句中的谓语必须是系动词；若为行为动词,则从句中的关系代词只能用which.
7. 先行词和关系词二合一
1)Whoever spits in public will be punished here. (Whoever 可以用 anyone who 代替)
2)The parents will use what they have to send their son to technical school. (what 可以用all that代替)

8. what/whatever;that/what; who/whoever
1）what = the thing which；whatever = anything
2) who= the person that whoever= anyone who
3) that 和 what
当that引导定语从句时 ,通常用作关系代词,而引导名词性从句时,是个不充当任何成分的连接词.宾语从句和表语从句中的that常可省略.What只能引导名词性从句, 用作连接代词,作从句的具体成分,且不能省略.
9. 关系代词that 的用法
1）不用that的情况
a) 在引导非限定性定语从句时.
b) 介词后不能用.
2) 只能用that作为定语从句的关系代词的情况
a) 在there be 句型中,只用that,不用which.
b) 在不定代词,如：anything, nothing, the one, all, much, few, any, little等作先行词时,只用that,不用which.
c) 先行词有the only, the very修饰时,只用that.
d) 先行词为序数词、数词、形容词*时,只用that.
e) 先行词既有人,又有物时,只用that.
三、名词性从句：

在句子中充当主语、宾语、表语与同位语的句子分别叫做主语从句、宾语从句、表语从句和同位语从句, 这些统称为名词性从句.

（一）主语从句
在复合句中用作主语的从句叫主语从句.
A 为了强调主语从句的内容,可将从句置于句首
B 大部分主语从句都可以用it作形式主语

为了保持句子平衡,主语从句常用it作形式主语,将主语从句后置.用it作形式主语的主语从句结构有如下几种：
1、It is + 名词 + that从句
2、It is + 形容词 + that从句
3、It + 动词 + that从句
4、It is + 过去分词 + that从句
用形式主语it引导的主语从句相当多,有些已形成固定的语法和译法.常见的有：
It is said that... 据说……
It is reported that... 据报导……
It is well known that... 众所周知……
It is announced that... 据宣布……
It is believed that... 人们相信……
It is thought that... 人们认为……
It is understood that... 自不待言……
It must be pointed out that... 必须指出……
It must be admitted that... 必须承认……
（二）宾语从句

宾语从句 The Object Clause,在复合句中作主句的宾语,它属于名词性从句.它可以作主句谓语动词的宾语,也可以作介词的宾语.宾语从句以从句的句式来决定连接词.

宾语从句有四步曲
连接词： （也叫引导词）
语序： 从句的词序用陈述语序（主+ 谓）
时态： 主句的时态如果是过去时,从句的时态应以过去时为基础作相应的变化.
人称： 要根据句中的意义作相应的变化

连接词（引导词）
从属连词 that ,if ,whether
连接代词 who, whom, whose, which, what
连接副词 when ,where ,how ,why
1.如果陈述句作从句,连接词用that,在口语和非正式语体中常可省略that .
2.特殊疑问句作从句,就用原来的特殊疑问词
3.一般疑问句作从句,连词用if或whether 在选择疑问句只用whether,记住这一结构：whether … or not .
（三）表语从句

表语从句放在连系动词之后,充当复合句中的表语.

A 可接表语从句的连系动词
可接表语从句的连系动词有be, look, seem, sound, appear等.
B as, as if / though引导的表语从句
C because, why引导的表语从句
what引导的主语从句表示结果或名词reason作主语时,后面的表语从句表示原因时要用that引导,不宜用because.
D 使用虚拟语气的表语从句
在表示建议、劝告、命令含义的名词后的表语从句,谓语动词需用"should+动词原形"表示,should可省略.常见的词有：advice, suggestion, order, proposal, plan, idea等.
（四）同位语从句

同位语从句用于对前面的名词作进一步解释,说明名词的具体内容.同位语从句一般由that引导,但也可以由whether以及连接代词和连接副词引导.

A 同位语从句一般跟在名词的后面
同位语从句一般跟在名词fact, hope, idea, news, doubt, suggestion, information, opinion, decision, discovery, truth, promise, statement, problem, rule等后面.
B 使用虚拟语气的同位语从句
在一些表示“建议、命令、要求”的名词后的同位语从句中,谓语动词用"should + 动词原形",should可省略.