3〕含有討論說(shuō)明或分析的問(wèn)題通常既要有主要推展素材，又要有次要推展素材。
2．4 寫好推展句的方法
主題句及關(guān)鍵詞確定后，開(kāi)始選擇和主題有關(guān)的信息和素材。實(shí)質(zhì)上，針對(duì)關(guān)鍵詞測(cè)試每一個(gè)所選擇的素材就是一個(gè)分類的過(guò)程。有一種常用的方法就是句子展開(kāi)前加以設(shè)問(wèn)，然后解答，即設(shè)問(wèn)－解答(why-because)的方法。下面我們通過(guò)舉例來(lái)看一看這種分類過(guò)程是如何完成的。例3：
假設(shè) (suppose) Topic sentence: English is an international language?
設(shè)問(wèn)(why) Why can we say English is an international language?
解答(because)
Because: English is spoken by pilots and airport control operators on all the airways of the world.
Because: Over 70 percent of the world's mail is written in English.
Because: More than 60 percent of the world's radio programs are in English.
Because: Pakistan was once one of the British colonies.
Because: Many members of the International Language Society are selected from English-spoken countries.
從上面可以看出，最初的三個(gè)推展句是和關(guān)鍵詞an international language一致的。第四句和主題句不統(tǒng)一，盡管第四句會(huì)成為另一主題句(Many Pakistanis speak English)很好的推展句。第五句說(shuō)服力不強(qiáng)。
當(dāng)然，在寫成段落時(shí)，沒(méi)有必要在每個(gè)句子開(kāi)頭寫上 "because"，但是，在動(dòng)筆展開(kāi)句子時(shí)，頭腦里要想著這個(gè)詞，這種檢驗(yàn)方法能幫助你把注意力集中在某個(gè)重心，圍繞主題思想層層展開(kāi)。