通常段落由二至三部分組成,即主題句，擴展句 和結尾句組成。主題句是段落的核心，它表明作者的觀點和態度，同時反映段落的中心思想。主題句的特點是：一是具有明確的觀點；二是具有一定的概括性。

    記住段落的中心思想應該是一個，要清楚地把它表達出來，盡量不要出現語言錯誤。如： Advertisement is an important link between producers and consumers today.\The library supplies people with knowledge of all kinds.\Nowadays ,the computer has found wide applications in many fields.以上句子都具備了主題句的特點，因為所有這些句子都可以用其它句子來解釋，描述，分析等即擴展句———主要圍繞主題句進行敘述。說明或論述，它是主題句發展成短落的主要組成部分。

    請看下面的段落： Nowadays ,the computer has found wide applications in many areas .It is used not only in caculations,but also in an engineering project,designing ,language learning,etc.In today's society ,computers can be seen working for us almost everywhere ,in shops ,banks ,post offices ,schools ,hospitals ,and so on .Computers have even entered most families .Children can learn various subjects on computers ,and parents can enjoy some entertainment from the computer,too.

    同學們可以看出本段的擴展句是：It is used not only ----后的四個句子 ，這些句子都緊緊圍繞主題句展開，敘述計算機在各個領域的應用，同時它們在語法和語義上是完整和連貫的，扣住了主題句的中心思想。

    結尾句是指用一句話將某段落的內容進行歸納總結，引發讀者對段落的進一步認識，請看下面段落： There are many problems with advertisements .Sometimes ,people consider them as a bad thing because many of the goods sound .Some advertisements are rather confusing ,and often deceive consumers into buying goods of poor quaity.The solutions to these problems is that a necessary law should be worked out .Otherwise some advertisements will be harmful to the society. 該段的結尾句是：The solution ----harmful to the society.最后一句說出了解決的方式及不加以解決會產生的不良后果。但要注意的是段落結尾句需要簡明扼要，并符合主題句的主旨，不過不能簡單的重復。

    以上是段落的基本寫作套路和方法，請同學們根據上述方法將下列主題句擴寫成60字左右的段落：
    1.Almost every big city in China has a serious traffic problem.
    2.Intoday's society,everyone needs friendships .
    3.Smoking is harmful to the health of people .
    最后祝愿同學們作文輕松考出好成績。