（一）句子种类概述
句子按种类可分为陈述句、疑问句、祈使句和感叹句。

（二）基础知识梳理
1．陈述句
陈述句用来说明事实或表示说话人的看法。
1)陈述句的肯定形式。如：
We are students.
We must obey the traffic rules.
We clean the room every day.

2)陈述句的否定形式
把陈述句改为否定句可以归纳为以下三种情况：
(1)在be，have，will，shall（包括情态动词）后直接加not。如：
We aren't students．
You needn't hand in your homework today.
(2)在助动词do，does，或did后加not，再把它们放在行为动词前面，而行为动词用原形。如：
We don't clean the room every day.
(3)否定句可由其他形式表示。如句中出现no，nobody，few，little，neither，hardly，nor，never等。如：
There are no books on the desk.
I can hardly answer your question.
Neither of the twins is a doctor.

2．疑问句
疑问句就是提出问题，让对方作出回答。英语中有四种疑问句，即一般疑问句、特殊疑问句、选择疑问句、反意疑问句。
1)一般疑问句
用于询问一个事实是否属实，其回答通常是Yes或No。其结构为：
be，will，have，助动词+主语+（主动词）/宾语
如：Is she a university teacher?
Will it be windy tomorrow?
Did he take part in the maths contest yesterday?

2)特殊疑问句
特殊疑问句对句中某一特定部分提问，以特殊疑问词开头根据实际情况，不必用Yes或No回答。常见的特殊疑问词有what，who，whom，when，what，time，where，why，which，whose，how old，how many+可数名词复数，how much+不可数名词，how long，how far，how fast，how soon等。其结构为：
疑问句+一般疑问句语句
如：Who has lunch fastest at school in our class?
What are you doing now?
How long have you lived here?

3)选择疑问句
选择疑问句通常提供两种或两种以上情况，询问对方选择哪一种。回答时选择一种，不必用Yes或No。
一般疑问句+A or B
如：Is there any coffee or water in the cup?
Do you often play basketball or play the piano?
特殊疑问句，A or B？ 或A，B or C？
如：Which is the biggest, the moon, the earth or the sun?
Which do you like better, the record or the ball?
4)反意疑问句
由两部分组成，前半句为陈述句，后半句是一个附着在前半句上的简短问句，回答时用Yes或No。它的构成和回答主要如下：
(1)肯定陈述句+否定附加疑问部分？
如：They are interested in collecting stamps, aren't they?
一Yes，they are. 是的，他们对集邮感兴趣的。
一No，they aren't. 不，他们对集邮不感兴趣的。
(2)否定陈述句+肯定附加疑问部分？
如：Tom didn't pass the exam, did he?
一Yes，he did. 不，他通过考试。
一No，he didn't. 9是，他没通过。

3．祈使句
祈使句表示请求、命令、叮嘱、邀请、劝告等。
1)祈使句的肯定结构
如：Come in，please.
Let me have a try.
Let's go to the cinema together.
2)祈使句的否定结构是在动词前面加上don't，
如： Don't be late for school.
Don't walk on the grass.

4．感叹句
1) 感叹句表达说话人说话时的惊异、喜悦、气愤等情绪。它常由what或how开头或引导。
感叹词What+强调部分（名词）+主语+动词谓语
如：What a mess picture it is!
What an exciting film we saw yesterday!
2) 感叹词How+强调部分（形容词或副词）+主语+动词谓语
如：How wonderful the film is!