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一，四种句子结构
众所周知，英语总共有四种句子结构，简单句(simple sentence),复合句(complex sentence),并列句(compound sentence)，并列复合句(compound-complex sentence.)
其实只要我们弄清了这些句子中的关键字，对于改写句子，我们就不难掌握了。
1. simple sentence是由单一主谓结构构成的句子，比较简单，如 I love you,够简单吧。简单句可以有一个或多个并列主语或动词，如：
Mary and Tom like the film.(此句中就有两个主语，但是仍是简单句。)
Mary like to watch TV and read book in weekend.(此句中有两个并列的动词。这个要注意与并列句compound-sentence区分开来。Mary like to watch TV and Tom like to read book. 这是两个并列的句子)
2.compound sentence是由两个或两个以上单句用逗号或并列连词连接起来的句子。以下各举一例。我们熟记这些并列连词的用法，改写句子的时候，遇到要改写为并列句的句子，如果没有把握，就挨个儿套一遍。这是比较笨的办法了，嘿!
-用逗号连接。exa.She went into the bathroom,she turned on the light. 这是由两个simple sentence用逗号连接的，就成了并列句，这是最最简单的一种。
-andexa.My son is sturdying English,and my daugter is studying French.这个句子中有两个主语，正在做的是不同的事，所以不能合并主语成为一个简单句。于是我们用一个and来连接两个句子。
-but但是 exa.At midnight,my classmate closed her book,but I studied until 2:0 a.m.
-for因为 exa. We are watering our trees,for the weather is too dry.
-or不然 exa. Put on your overcoat, or you will catch cold.
-NOR也不 exa. He cannot find anyone now,nor does he expect to find anyone in the future.
-SO所以 exa. The children started arguing ,so I turned off the TV.
-Yet然而 exa. He worked hard,yet he failed.
3.Complext sentence复合句是由简单句与从属连词引导之从句构成的。复合句我们也是常见的，我们要特别注意的是连词的用法，以下也举一部分例子。建议去网上找一些相关习题来多多练习，正所谓熟能生巧嘛。
-That The bridge that across the river was built in 1990. that引导的定语从句修饰The bridge.
-Which My mother bought me a present which was a skirt.
-What What you want has been sent here.
-Whose The girl whose hair is red named Lisa.
-Who : Who borrowd my pencil is unknow
-When : When storm hit the city,wecrisscrossed the window with strong tape.
-Where : It's the place where we met the first time.
-Why : Nobody can explain the reason why he comes late.
-Since: Since you're not interested, I won't tell you about it.
-Until: Until the sun went down,we stayed on the beach.
-If : If that is true, what should we do?
-Though: Though I have tried my best to do,I still failed.
-Because : Because the weather is very bad,the party be canceled.
4.compound-complex sentence并列复合句是由两个或多个单句和一个或多个从句构成的句子。有人说并列复合句是最难的，其实不然，只要你懂了并列句，和复合句，并列复合句也就手到擒来了。其实就是并列句和复合句的总和嘛。两个或多个复合句用适当的并列连词一连，不就成了并列复合句了?下面就只举一个例子。
-将下列句子改写成并列复合句
Jack dialed the police emergency number. He received a busy signal. He dropped the phone and ran. He didn’t have time to call back.(compound complex sentence)
Answer: Jack dialed the police emergeney number,but he receiving a busy singal ,so he dropped the phone and ran because he didn't have time to call back.
此句中用了一个but和so做并列连词，用了一个because 引导的原因状语从句。
"Jack打警察局的紧急电话。只听到忙音。他挂上电话就跑。他没有时间再打了。" 如果只是这样几个散句，就很没有连贯性。打电话但是只听到忙音，于是我们可以用一个but来连接，那么他挂上电话往外跑，是因为忙音所以他挂了电话跑，于是我们可以用一个so连接，那他为什么挂上电话跑呢?因为他没有时间再重打，于是我们就用一个because. 比较笨的办法就是这样把他的中文意思领悟了，弄清其中的关系，那再用我们前面学到的并列句和复合句结合起来，就完成了并列复合句了。
二，平行结构parallel structure.
平行结构是把两个以上意思并列的成分用同等的语法形式表达出来，他可以是单词，词组，从句，也可以是句子。
常见的句子结构如下例子供大家参考。
either/or不是...就是: Either my sister or I will go to the party.
neither/nor既不...也不: She is neither young nor inexperienced.
not only/but also不止...而且: Not only does he like reading,but also he can even write some.
both/and两者都: Both newyork and London have trffic problems.
whether/or 是...还是: Whether she wins or loses,this is her last tournamen.
although/yet 尽管...还是: Although he had overtime work last night,yet he wasn't finished his project.
if/then如果...那么: If you study hard,then you will pass the exam.
