英语当中句子按使用目的可分为：
- 陈述句：用来阐述观点、说明事实或表明看法、态度等。eg：He arrived quite early.(事实)他很早就到了。He can’t have missed his train.(看法)他不可能误了火车。
- 疑问句：用于提出问题。英语中有以下三种疑问句：1. 一般疑问句：以一个助动词、情态动词、动词be或have开始，通常要求以certainlyperhapsnot at all等)回答，句末用问号,读音时读升调。eg:Can you finish it on time?Are you Tom's brother?2. 特殊疑问句：又叫“wh—疑问句”，这种问句都以一个疑问代词或疑问副词开头。wheredo you live?What caused the accident?3. 选择疑问句：这种问句提出两个答案看哪一个是正确的，在结构上和一般问句差不多。Shall we go home or stay here for the night?Do you want tea or coffee?
按句子结构可分为简单句、复合句、并列句三类：
- 简单句：只包含一个主谓结构的句子叫简单句：
Think more.
Lucy and I always go to school together.
They sang and danced to their hearts"content.
- 并列旬：包含两个或两个以上互不依从的主谓结构的句子叫并列句用并列连词或分号来连接。
Honey is sweet,but the bee stings.(谚语)
It is raining heavily,the sports meeting hs to be called off.
- 复合旬：由一个主切和一个及以上的从句构成的句子叫复合句导，从句充当主句的主语、宾语、表语、定语、状语、同位语等。
What they had seen there impressed them deeply.(主语从句)
We should never pretend to know what we do not know.(宾语从句)
Her suggestion was we finish the project at any cost.(表语从句)
This is the very man Imet the other day.(定语从甸)
This film had begun when we got to the cinema.(状语从句)
We all know the truth that the earth is round.(同位语从句)
句子分类明白之后，我们要搞清楚what、when、why、do、where的用法：
what、when、why、where可以做疑问副词或者疑问代词，而无论是哪种情况，根据上面句子分类部分的说明，我们知道他们都有置于句首的可能，具体而言：
- 简单句中的特殊疑问句，what、when、why、where必须放在句首使用，此时，what做疑问代词，后三者为疑问副词;
Where are you going?
What kind of movie do you like?
- 复合句中的主语从句，疑问代词(what, who, whose, which, whatever, whichever ,whoever等)可以放在句首:
What makes me angry also makes you angry.
Who broke the window should be punished.
do 作为助动词，用在句首的情况只有两种：
- 一般疑问句：
Do you remember me?
- 祈使句：
Do it！-----表示命令
Do me a favour, please. ------表示请求
Ok，希望能帮到你，我是@Rex老师吖，欢迎关注！谢谢！
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