运用因果法时，可采用先因后果或先果后因两种模式；若有多个原因且有主次之分时， 可考虑按照从主到次或从次到主的顺序来阐述各项内容。例如：Some countries have banned smoking in many public places and office buildings, and they see strong reasons for this. The first and most important reason is that while limits on smoking restrict the rights of smokers, smoking itself affects the rights of non-smokers. Studies have shown that second-hand smoke can have a harmful effect on the health of non-smokers, Second, aside from the long-term health effects of second-hand smoke, it can have very serious immediate consequences for those who are allergic to it. Third, the ashes and cigarette butts left behind by smokers are another form of pollution. They dirty our environment and, as taxpayers, we must all Day for the cleanup of our public places.本段以先果后因的形式展开。主题句（第一句）先提出事实，即有些国家已经禁止 在许多公共场所吸烟，并用关键词reason引导出造成这一事实的三个理由，并根据其重 要性上按照从主到次的顺序依次表达。2. 因果法常用词语because, because of, since, for, owing to, thanks to, on account of, due to, be due to, be a consequence of, result from, be the result of; as a result, consequently in consequence, therefore, accordingly, for this reason, so, thus, lead to, contribute to, result in, cause, be the reason forV. Classification （分类法）分类法多见于说明文或议论文的说明部分，它是指先把同一事物按一定标准分类， 再分别进行详细说明的扩展方法。运用分类法时，应注意保持分类标准的统一性，不能 在段落中间随意改动。例如：There are three kinds of book owners. The first has all the standards of sets and best-sellersunread, untouched, The second has a great many booksa few of them read through, most of them dipped into, but all of them as clean and shiny as the day they were bought. The third has a few books or many every one of them dog-eared and dilapidated, shaken and loosened by continual use, marked and scribbled in from front to back.本段采用分类法，按照藏书人所读书籍多寡的标准，把藏书人分为三大类进行具体说明。Part Three Various Forms of Writing (from appreciation to production)I. Wring based on topic sentences (段首句作文)1. 写作技巧1.1认真审清标题和主题句，仔细分析研究标题与各主题句之间的关系，把握全文的主题。1.2充分理解主题句，以明确每段的写作重点并弄清各段之间的逻辑关系，使主题表述清晰 流畅。1.3根据标题和主题句选择与其关系最密切、最具说服力、最容易表达的细节、例子等围绕 主题句进行扩展。2. SampleDirections: Write a composition entitled aMy Idea of Internet9f in three paragraphs. You are given the first sentence of each paragraph and are required to develop its idea in completing the paragraph. Write no less than 120 words.My Idea of InternetInternet plays an important role in our life. Yet, Internet is not flawless.There is no doubt that Internet has contributed and will contribute greatly to our life.2.1 AppreciationMy Idea of InternetInternet plays an important role in our life. When you surf the net, the world seems smaller than ever, and countries far away seem no farther than your hometown. Every hour, thousands of people, including young children, university students, scientists, businessmen, see various information through Internet. You can discuss international affairs, football games, or your viewpoint on love and marriage with known or unknown people. In this way, you may make some fYiends, who share common views with you, And whats more, various meetings can also be held on the net. What a wonder! many people do exclaim, Indeed, Internet is one of the most wonderful human inventions.Yet, Internet is not flawless. First, there are too much rubbish on the net. Some people are just over-enthusiastic to offer worthless information, This, in turn, has made it more and difficult to find what you want. Secondly, officials also find it hard to prevent Internet form the invasion of criminals. To some extent, it actually makes it more convenient to commit certain crimes. And sometimes the cost is so prohibiting to many Chinese people, So we can see, just like most other inventions, Internet has its own problems.There is no doubt that Internet has contributed and will contribute greatly to our life. We should make full use of it while minimizing its negative effects, I think a stricter administration will be of considerable help in making better use of Internet.2.2 AnalysisFramework of the essay （文章框架结构）Para. 1因特网的作用TS （topic sentence） Internet plays .in our life.DS （developing sentences）1. When we surf . hometown.（作用一：世界变小）2. Every hour . through Internet.（作用二：获取信息）3. You can . with you.（作用三： 交友）4. And whats more,. the net.（作用四：网上会议）TrS （transitional sentence）What a do exclaim.CS （concluding sentence） Indeed, Internet. inventions.Para. 2因特网的局限/问题TS: Yet, Internet is not flawless.DS: 1. First. you want.（问题一）2. Second, . crimes. （|、可题二）3. And sometimes. Chinese.（问题三）Para. 3因特网之我见TS: There is no doubt. in our life.DS: l.We should make .in our life.（建议一）2.1 think . effects.（建议二） Useful Pattern Drills1. When you surf the net, the world seems smaller than ever, and countries far away seem n farther than your hometown.2. Second, officials also find it hard to prevent Internet from the invasion of criminals.3. I think a stricter administration will be of great help in making better use of Internet.