第一单元 段落简介
1．1段落
段落是构成文章的一组句子。段落必须表达完整的意思：或描写事物（describe something），或争论某事（argue about something），或对某事提出疑问（question something），或要求什么（demand something），或给事物下定义（define something），或驳斥某观点（reject something）。
1．2典型段落的构成
一个典型的段落通常由三部分组成：（1）主题句（the topic sentence）；（2）说明或支持主题的推展句（ supporting sentences）；（3）结论句（the concluding sentence）（有些段落没有该部分）。
示范段落1-1
We all know that cigarette smoking is a dangerous habit because it causes health problems． Doctors say it can be a direct cause of cancer of the lungs and throat and can also contribute to cancer of other organs． In addition， it can bring about other health problems such as heart and lung diseases． It is clearly identified as one of the chief causes of death in our society．
1．3示范段落分析
这是一个典型的段落，可概括提纲如下：
主题句： We all know that cigarette smoking is a dangerous habit，because it causes health problems．
推展句： 1． Doctors say it can be a direc cause of cancer of the lungs and throat and can also contribute to cancer of other organs．
2． It can bring about other health problems such as heart and lung diseases．
结论句： It is clearly identified as one of the chief causes of death in our society．
从以上提纲可见，主题句提出了一个问题： What kind of health problems does cigarette smoking cause？随后的两个推展句回答了这个问题，结论句总结了推展句并再一次强调主题句。
Exercise 1-1
Directions： Read the following paragraphs and find out the topic sentence， the supporting details and the concluding sentence， if there is one．
（1）
The need for wildlife protection is greater now than ever before．About a thousand species of animals are in danger of extinction,，and the rate at which they are being destroyed has increased． With mammals， for instance， the rate of extinction is now about one species every year； from A． D． 1 to 1800， the ratewas about one species every fifty years． Everywhere， men are trying o solve the problem of preserving wildlife while caring at the same time for the world’s growing population．
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