句子结构
句子有两种分类标准。一种是按照句子的使用目的分类，可分为陈述句、疑问句（一般疑问句、特殊疑问句、选择疑问句和反意疑问句）、祈使句和感叹句；另一种是按照句子结构分类，可分为简单句、并列句和复合句。在这里我们重点分析一下简单句、并列句和复合句之间的区别、连接手段和注意事项。
简单句simple sentence 1. 定义：只包含一个主谓结构的句子叫做简单句。
1) 陈述句declarative
An Olympic Marathon is 26 miles and 385 yards, approximately the distance from Marathon to Athens.
2) 疑问句question
a) 一般疑问句general question
例：Have you read this book? （你读过这本书吗？）
b) 反意疑问句tag-question
例：If I mistake not, you used to cook your own food, didn\'t you you?
2. 注意事项：如果一个句子里出现两个或更多主语共同使用一个谓语，或一个主语后面接两个或多个谓语，或者两个主语后面接两个谓语，我们都应视其为简单句。
C) exclamatory
What a sunny day! How beautiful you are!
并列句：co-ordinate 定义：包含两个或多个互不依从的主谓结构，通常由一个或多个并列连词来连接的句子叫做并列句。
1. 联合combine关系的并列句由and, nor, neither…nor和not only …but also等连接；
Turn on the television or open magazine and you will often see advertisements showing happy, balanced families.
在这种用法中，and前面部分通常是祈使句，and后面的句子用将来时，表示“会”。
2. 转折shift关系的并列句由but, however, while, even so，still和yet等连接；
While I admit that there are problems, I don\'t think that they cannot be solved.
While在此为连词，表示语气的转折，意思是“尽管、然而、但是”。
John seems a nice person, though I don\'t trust him.
though（可是）虽然可用作表示转折意思的副词，但它通常置于句尾或插入句子中间。
3. 选择alternation关系的并列句由or, otherwise, either……or等连接；因果关系或推论关系的并列句由for, therefore等连接。
例：Dress warmly, or else you\'ll catch cold.
复合句compound定义：包含两个或多个主谓结构，并且，其中一个主谓结构充当主句，另一个或多个主谓结构为从句，充当该主句的主语、表语、宾语、定语或状语，这样的句子叫做复合句。
名词性从句
1. 主语从句subject
在整个句子中充当主语成分的从句。可以由从属连词that, whether等引导；也可以由连接代词what, which, who以及由连接副词how, when, where, why，等引导。
It is known to the world that Mark Twain is a great American writer.
In some countries what is called "equality" does not really mean equal rights for all people.
2. 同位语从句appositive
从句的作用是做主语、表语或宾语的同位语（即，不是对主语、表语或宾语进行修饰和限定，而是说明其内容含义），则叫做同位语从句。由that引导。
The mere fact that most people believe nuclear war would be madness does not mean that it will not occur.
A) what C) that B) which D) why
可以由同位语从句修饰的名词还有thought, idea, news, hope, belief, doubt等。
3. 宾语从句（包括间接引语）object
在主句中充当宾语成分，即跟在及物动词后面、不及物动词加介词后面，或介词后面的从句叫做宾语从句。可以由从属连词that, whether, if等引导；由连接代词what, which, who等引导；由连接副词how, when, where, why等引导。
例：Professor Lee\'s book will show you how what you have observed can be used in other contexts.
注意：由于宾语从句有时会造成整个句子的结构失去平衡，所以可将宾语从句后置，使用it做形式宾语。
例：They have discussed it for about a whole day whether we are to be allowed to take part in that concert.（他们就我们能否获准去听那场音乐会这件事已经讨论了几乎一整天。）
2) 连词what为缩合连词，相当于all that/ everything that
•lWater will continue to be what it is today---next importance to oxygen.
形容词性从句
4． 表语从句predicative
当主句的谓语是系动词，而从句位于其后，即在整个句子中充当表语，则该从句叫做表语从句。可以由从属连词that, whether等引导；由连接代词what, which, who等引导；由连接副词how, when, where, why等引导；以及由because等引导。
Their argument was how we know a way to test the authorities statement.（他们的论据是我们怎能知道检验权威观点的方法。）
例：Water will continue to be what it is today ------- next in importance to oxygen.
“水在将来还是现在的状况--其重要性仅次于氧气。”
5. 定语从句attributive
如果从句用于修饰主句的名词（主语、宾语或表语），则其句子成分为定语，叫做定语从句。定语从句分为两类：非限制性定语从句和限制性定语从句。前者用逗号与主句隔开，如果去除这一部分并不改变影响主句的意思的定语从句（在非限制性定语从句中，需要注意的是，不能用that替换which引导词）。而限制性定语从句正好与之相反，不需逗号将从句与主句隔开，如果去除的话，将大大影响原句要表达的意思。
指代人时，定语从句可以由关系代词who, whom, whose引导；指代物时，可以由关系代词which引导；指代人或物时，由that引导；由关系副词when, where, why等引导。
The residents, all of whose homes had been damaged by the flood, were given help by the Red Cross.
“那些房屋全部被洪水毁坏的居民得到了红十字会的救济”。
As is announced in today\'s papers, the Shanghai Export Commodities Fair is also open on Sundays.
注意：
a) 关系代词whom, which, that在从句中做宾语时，常常可以省略，在口语中更常见。
b) 引导词where就等于介词加which，都指代从句的地点状语。Where本身就可以代替介词短语表示地点状语，而which只能指代介词短语中的名词，所以它前面或从句中必须有介词。同样的情况还有what和anything/ the thing that/ which。前者等于后者。
例：This is the house where / in which I used to live.（这就是我曾经住过的房子。）
This is what / the thing he told me just now.（这就是刚才他告诉我的事情。）
•不能使用 that 引导定语从句的几种情况：
•a) 非限制性定语从句
•b) 关系代词在从句中作介词的宾语，介词提前时；I need a pen with which I will write a letter.
•c) 在 such 之后出现的定语从句只能用 as 引导。There are as many books as are needed
•只能用 that 引导的定语从句：
•a) 先行词为指物的不定代词 (除 something)；例如：•All that is needed is a continuous supply of the basic necessities of life.
•但是，指人不定代词（如all）后要用who。例如：•All who want tickets should go to the office.
•b) 先行词前有 only 修饰时；例如：•Miss Lister is the only one of those girls that is from France
•c) 先行词前有最高级或序数词修饰语时；例如：•Shakespeare is the greatest poet that England has ever had.
•d) 先行词受强调型形容词 very 修饰时；例如：•That\'s the very reason that I will help you.
•e) 先行词受 same 修饰（更多的是使用 as 引导）时；例如：•Mother bought me the same present that she had sent you on your birthday.•
f) 先行词为两部分，一部分指人，一部分指物时。例如：•He talked brilliantly of the men and books that interested me.•
•as 作关系代词的用法：•
a)将其置于句首或句后，用逗号与主句隔开，引导一个定语从句，有时甚至用省略句，它指代的往往是整个主句的内容。例如：•They opposed the idea strongly, as could be expected.
•b)“the same(...)as”结构。例如：•It is said that the moon is made of the same kind of matter as exists on the earth.
•c)“such(...)as”结构。例如：•She isn\'t such a careless student as you think she is.•要将这个结构与“such(...)that”结构（表示目的或结果）区别开。•Tom is such an efficient worker that his boss has promoted him twice.•Tom isn\'t such an efficient worker as you told us.•〖注意：as 在定语从句中担任名词性成分；that 在状语从句中不作成分。〗
•d)“as...as”和“so...as”结构。例如：•. •We witnessed so great a parade as nobody ever dreamt of in ancient days.•
•关系代词 which 引出非限定性定语从句
•其先行词可以是前边的整个句子或者句子的一部分。当它代替前边的整个句子时，其意义相当于and this。
•The sun warms the earth, which makes it possible for plants to grow.
•It was raining hard, which prevented us from attending the conference.
•as 和 which引出非限定性定语从句的区别
•1） which不可位于句首。 as引导的分句位置灵活。
•2）as在从句中作主语时，其后功能词必须是be或其它系动词。
•Helen was much kinder to her youngest child than she was to the others, ___of course, made the others jealous. A)who B)that C)what D)which （四级，93年6月）
•3）which在从句中作定语，其前可以有介词。
•I called him by the wrong name, for which mistake I apologized
句法结构
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