1.主题句的特点
　　主题句是全段的核心。它由中心词和限定词两部分组成。中心词说明讨论的主题（topic）是什么，限定词是把主题具体化，它限定讨论的内容，范围和展开方式等。例如：
　　The first key factor to success is diligence， (what) which simply means no waste of time.
　　主题 限定词 限定词
　　I think you will make the decision according to the following factors.(how)
　　主题 限定词
　　考生可通过回答How？Why? Where? What?等问题来把主题具体化，选定限定词。主题句的展开通常会出现如下问题：
　　（1）过于空洞。只给出主题，未指出写作内容和展开方式。如：
　　The relationship is not good.此句可以通过回答what kind of relationships，to what extent等问题将之具体化。可改为：The relationship between family members is not as close as before.这样主题句限定了关系的范围，文章后面的开展方式–侧重于现在关系的不好，又可以用对比的方式展开。再如：
　　Clothes play a part in our life.此句没有限定写作的大体内容或方式，（是衣服的时尚性，还是实用性），读者不能预测下文的展开方向。通过回答”how”这样的问题，我们可将主题句具体化。改为：Clothes play a critical part in the conclusions we reach by providing clues to who people are。修改后的句子点出了文章的写作内容–根据服装，可以判断人。
　　（2）过于具体。太具体的主题句使段落后面没有展开的余地。如：
　　He thought highly of her and helped her to find jobs of teaching at several institutions.
　　这种叙述性的句子，对事实的陈述过于详尽，不适合做主题句。
　　2.主题句的位置
　　（1）位于段首，也就是开门见山。把主旨放在段首，使读者对文章内容、结构等有个把握。在应试中，这是十分行之有效的方法 。如：
　　From the health point of view we are living in a marvelous age. We are immunized from birth against many of the dangerous diseases. A large number of once fatal illnesses can now be cured by modern drugs and surgery. It is almost certain that one day remedies will be found for the most stubborn remaining diseases. The expectation of life has increased enormously.
　　段首主题句清晰地点出本段的中心思想，后面从对疾病的免疫、治疗，及对疾病的攻克三个方面说明健康医疗状况良好。读者只看段首就可抓住段落主旨。
　　（2）位于段中。主题句出现在中间，起到承上启下的作用，上文引出背景，下文可以用于分析。如：
　　Before China's entry into the WTO，the common people were optimistic about what access would mean，believing that if joining were not beneficial，the government would not have spent 15 years negotiating for its entry. They were perhaps thinking that when the day came，the price of phone calls would be lower，and also house rents and that insurance services would be better. But they neglect the prospect of unemployment and other domestic crisis.Since China joined the WTO，some people，owing to advanced age and limited experience，may find it difficult to keep their work.
　　文章开始铺垫了一个对待入世的积极的期待，而中间的主题句将文风一转，引出主旨：入世带来的消极方面。然后文章从失业开始进一步展开论证。
　　（3）位于段末。主题句位于段末，既可以点题，也可以总结上文，给读者留下深刻的印象。如：
　　Ms. Yang，aged 50，works as a cleaner in an office building，and her annual income is about 20 000 yuan.She has signed up for an English language training course，the cost of which is much more than her annual income. Why English? English-based success stories have indicated to the Chinese that English means opportunities，wealth，and prospects.
　　本文先举了杨女士花钱学英语的例子，然后引出问题：为什么要花如此高价学习英语。段末给出结论，点出学习英语的重要性。结尾点题，给人以深刻的印象。