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1． 主題句
主題句（topic sentence）是表達段落主題的句子。它用以概括段落大意，要求全段其他文字都圍繞它展開。請看下例：
My mother has passed along to me certain rules for getting along with others. Don't argue with parents; they will think you don't love them. Don't argue with children; they will think themselves victimized. Don't argue with spouses; they will think you are a tiresome mate. Don't argue with strangers; they will think you are not friendly. My mother's rules, in fact, can be summed up in two words: Don't argue.
主題句中提出的 "certain rules" 指的是什么？展開句中通過四個 "Don't argue --" 逐一加以交代。從結構來看，這是一個比較典型的段落，它包括了主題句，推展句和結論句（即本段中的末句）。
1．1 主題句的位置
主題句通常放在段落的開端，其特點是開門見山地擺出問題，然后加以詳細說明。其作用是使文章的結構更清晰，更具說服力，便于讀者迅速地把握主題和想象全段的內容。主題句可以放在段中起到承上啟下的作用，或放在段尾起概括全段的作用。但初學者比較難于掌握，因而在四級考試中，考生應盡量采用將主題句放在段落開頭的寫作手法。，
例1: Our life today depends very much on energy. In towns and in villages, on farms and in factories, machines have made life easier than it used to be. The machines use energy, and energy is needed for heating, lighting, communications, carrying goods -- everything. Factories and industrial plants use a great deal of energy to make the things that we use and buy and sell.，
這段文字所講的主要是能源問題。第一句就概括性地提出“我們目前的生活很大程度上依賴于能源”。而隨后出現的三句都是具體事例，對第一句進行說明和論述。我們可以斷定第一句為該段的主題句（斜體部分）。 ，
例2: （主題句）No one can avoid being influenced by advertisements. （推展句1）Much as we may pride ourselves on our good taste, we are no longer free to choose the things we want, for advertising exerts a subtle influence on us. （推展句2）In their efforts to persuade us to buy this or that product, advertisers have made a close study of human nature and have classified all our little weakness.
以上這段由三句話組成。第一句是主題句，直截了當指出無人不受廣告影響這個主題，接著列舉兩個推展句對其補充和支持，指出我們已無法自由選擇所需的商品，理由是廣告商已仔細研究了我們的心理，并完全掌握了我們的弱點。句子銜接自然，步步緊扣主題。
