就结构而言,英语句子有4类：简单句（the simple sentence），并列句（the compound sentence）；复杂句（the complex sentence）；并列复杂句（the compound-complex sentence）。
只有一个主语（subject）和谓语（predicate）的句子，叫简单句。两个或两个以上的简单句，由等立连词（coordinating conjunction）and, or, but, so, for等连接的句子，叫并列句。例如：
① You can go there and see the manager.
② I like reading, but she likes singing.
③ Take it or leave it.
由一个主句（main clause）和至少一个从属分句（也称从句, （subordinate clause）合成的句子，叫复杂句。根据性质和功能，从句有3种，即：㈠ 名词从句（the noun clause）；㈡形容词从句（也称定语从句, the adjective clause, or the relative clause ）；㈢副词从句（也称状语从句, the adverb clause）。
如果一句里有两个或以上的并列句，再加上至少一个从属分句，这种句子就是并列复杂句。
从属分句的共同点是，它们都要由从属连词（subordinating conjunction）引导而出。
名词从句主要由That引导，如：
④ He told me that he was unwell yesterday.
⑤ That China is a big country cannot be denied.
⑥ The problem here is that people tend to be indifferent to politics.
④里的名词从句是主句的宾语；⑤里的是主句的主语；⑥里的是主句的补足语。
形容词从句由关系代词who, which, that等或关系副词 when, where, why等引导。这里的关系词和从属连词不同的地方是关系词既是连词也是代词或副词。形容词从句的功能在修饰主句里的名词，叫先行词（the antecedent）。例如：
⑦ Do you know the man who is speaking to that lady?
⑧ Show me the evidence which you have gathered.
⑨ The puppy that was knocked down has just been taken away.
⑩ Is this the place where we will meet?
● Sunday is the time when working people can relax a bit.
必须注意的是，先行词是人，就由who或that引导；如果是动物或东西，就用which或that；如果是 所有格（the possessive case），就用whose；如果是地点、时间、原因，就要分别用关系副词where, when, why。
至于副词从句，可以根据从句的性质选用从属连词。
时间副词从句用when, as等，如：
● John received a warm welcome when he returned.
● As he came up the stairs, she went out.
原因副词从句用because, since等，如：
● Tom could not come because he was ill.
● Since the rain has stopped now, let us go out.
条件副词从句用if , unless等，如：
● If you work hard, you will succeed.
● I wont go unless I am invited.
让步副词从句用although, though等，如：
● The Lees are generous though they are not rich.
● Although it was hard work for us, we enjoyed it.
地点副词从句用where, wherever等，如：
● Please stay where you are.
● Wherever I go, I meet friends,
此外，还有些副词从句，如比较的、状态的、目的的 、结果的，都由不同的从属连词引导。
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