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      句子是作文的基本单位，它由词按语法规律构成。一个句子表达一个完整的思想，一篇优秀的作文是由论述清晰、合乎语法规则的句子所组成的。打好句子基础，是提高写作水平的关键。对句子结构和特征的正确理解，有助于写出好的句子。

　　一、句子的完整性

　　句子的基本结构是主谓结构，一个没有主语或谓语的句子是不完整的。在复合句中，从属句或短语是句子的一部分，也是不能独立存在的。如：When he was young. 这就是一个不完整的句子。要使它有意义，必须附属在主句上，可以将其改为：When he was young, he lived in the countryside.句子中省略某些必要的，有助于理解的词，也会造成句子的不完整。例如：Then a gentleman in black came out the room.走出屋子应表达为“come out of the room”，这样才使句子结构完整。句子的完整性还包括句意的完整性，即句子不论长短，只能有一个中心思想。例如：I was walking in the street yesterday morning, and encountered an old friend.这个句子没有完整的句意，不符合只能有一个中心思想的写作要求，可把它改写为主从句：Yesterday morning, when I was walking in the street, I encountered an old friend.

　　二、各种不同的句子开端

　　一般情况下，句子的主语放在句首。但是，如果所有的句子都以主语开头，文章就会变得单调。为了避免这种情况，应使用不同的句子开端。除主语外，形容词或副词、现在分词短语、过去分词短语、动词不定式短语、介词短语、从句等都可以放在句子的开头。例如：

　　①Cheerful, efficient and warm-hearted, they will do everything to make your tour smooth and comfortable.

　　②Certainly we should try our best to help them.

　　③Sure enough, he passed the exam.

　　④Talking about many of the bad

effects of the automobile, he began to advise us to ride bicycles to protect the environment of the city.

　　⑤Moved by his speech, I was momentarily at a loss what to say.

　　⑥To know something about English is one thing; to know English is quite another.

　　⑦By speaking English everyday and every-where, he mastered spoken English in a short period of six months.

　　⑧If you will help me, I can finish the job in two hours.

　　三、句子的一致

　　句子的一致指一个句子中人称、数、语气、时态和语态应保持一致，否则这个句子就会逻辑混乱，意义模糊。例如：

　　①One reason that I appreciate classical music is the enjoyment and relaxation you get from listening to it.

　　②No one should be forced into a career that they believe is not suitable for them.

　　这两个句子应改为：

　　①One reason that I appreciate classical music is the enjoyment and relaxation I get from listening to it.

　　②No one should be forced into a career that he or she believes is not suitable for him or her.

　　在一些特殊情况下，主语和谓语保持一致应特别引起注意。

　　（1）no one, each, either, neither, the other, more than one, many a等作主语时，谓语动词用单数。例如：

　　More than one man watches the game.

　　（2）along with, together with, as well as, in addition to 和no less than 这些词组不起并列连词的作用，当它们前面的主语为单数时，不管后面的名词或代词是单数还是复数，谓语动词仍用单数。例如：

　　He, as well as the other students has learned how to write a letter.

　　（3）集体名词如people, police, militia, crew, cattle等作主语时，后接复数动词；furniture, luggage, clothing, machinery, equipment等作主语时，谓语动词用单数。既可接单数动词又可接复数动词的集体名词有army, audience, class, committee,company, family,government, jury, party, team等。

　　（4）当一个句子的两个主语由or, either…or, neither……nor, not only……but also等连接时，谓语动词要与邻近的主语一致。例如：

　　Neither his classmates nor Tom has understood this word.

　　四、句子的标点符号

　　标点符号可以使句子的意思表达得更清楚。

　　英语写作中常用的标点符号有：句号、问号、叹号、逗号、冒号、引号。句号、问号、叹号用在句子末尾，表示较长的停顿。在陈述句和祈使句后用句号，在疑问句后用问号，在感叹句后用叹号。例如：

　　①It’s a fine day.

　　②Is it a fine day?

　　③What a fine day!

　　逗号表示一个短促的停顿。它可以隔开同位语、独立成份、分词短语以及放在句首或插在句子中间的状语从句等。例如：

　　①This is Mr.Smith, the president of the university.

　　②This, I think, was mainly due to his illness.

　　逗号还可以连接一个句子中的平行成分，如主语、谓语、表语、宾语、定语、状语等。例如：

　　①He, Tom and I were all interested in this book.

　　②He got up, washed and hurried to school.

　　③He was kind, good-tempered and easygoing.

　　五、句子中常用的一些短语

　　了解和记住一些常用的短语，可以使句子更为生动形象、符合逻辑。

　　（1）表示介绍、引出观点的一些短语：in the eyes of, in my opinion, as we know, as far as……be concerned, in general, in most cases, it is said that……, it is reported that……, it is estimated that……

　　（2）表示递进、转折、强调或比较的一些短语：at first sight,at first thought, as a matter of  fact, in fact, nevertheless, however, in contrast, on the contrary, compared with/to,namely,in other words, that is to say.

　　（3）表示举例、列举的一些短语：for example, for instance, such as, first, firstly, in the first place, at first, first of all, in the mean time , at the same time, and so on.

　　（4）表示原因，结果和结论的一些短语：as a result of, on account of, owing to, therefore, as a result, in consequence, consequently, thus, all in all, first and last,by and large, on the whole, in a word, in short , in brief.

　　总之，短句的写作是英语写作的基础，它需要正确理解句子的结构和特征，也需要足够的练习和平时的积累。除去以上所述技巧外，还应多读、多练、多记，掌握的知识和素材越多，就越容易写出好的句子。