2.1 主要推展句

主要推展句(major supporting statement)的主要特点是：围绕段落主题句展开的每一个推展句本身都不要求作进一步的说明或证明，句与句之间的关系是相互独立又是互相连接的。

例1：(主题句) There are several factors affecting climate. (推展句1)One factor is the mount of sunlight received. (推展句2)Altitude, or the height above sea level, also determines climate. (推展句3)The oceans have an effect on the climate of adjacent land. (推展句4)In addition, climate is influenced by the general circulation of the atmosphere.

主题句指出影响气候的几个因素。然后用四个扩展句说明四种因素。第一种是太阳光的接收量，第二种是海拔高度，第三句和第四句分别是海洋和大气环流因素。

2.2 次要推展句

次要推展句(minor supporting statement)是指对主要推展句作进一步的事实分析和举例说明。它从属于某一个或某几个推展句。

例2：(主题句)I don't teach because teaching is easy for me. (主要推展句1)Teaching is the most difficult of the various ways I have attempted to earn my living: mechanic, carpenter, writer. (主要推展句2)For me, teaching is a red-eye, sweaty-palm, sinking-stomach profession. (次要推展句1)Red-eye, because I never feel ready to teach no matter how late I stay up preparing. (次要推展句2)Sweaty-palm, because I'm always nervous before I enter the classroom, sure that I will be found out for the fool that I am. (次要推展句3)Sinking-stomach, because I leave the classroom an hour later convinced that I was even more boring than usual.

从属于主要推展句2的三个次要推展句起着解释说明作用，分别解释red-eye, sweaty-palm, sinking-stomach的含义，这就更加形象生动地证明了 "teaching is not easy" 这个主题。

2.3 主要推展句与次要推展句的关系

主要推展句与次要推展句的关系(relation)基本可以遵循下面的“三部分”(three-part)规则。

1〕每个主要推展句都应该是对主题句中表示主要思想的关键词的直接、明确的说明。

2〕每个次要推展句都应该说明它的主要推展句。

3〕含有讨论说明或分析的问题通常既要有主要推展素材，又要有次要推展素材。

2.4 写好推展句的方法

主题句及关键词确定后，开始选择和主题有关的信息和素材。实质上，针对关键词测试每一个所选择的素材就是一个分类的过程。有一种常用的方法就是句子展开前加以设问，然后解答，即设问-解答(why-because)的方法。下面我们通过举例来看一看这种分类过程是如何完成的。例3：

假设 (suppose) Topic sentence: English is an international language?

设问(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.

从上面可以看出，最初的三个推展句是和关键词an international language一致的。第四句和主题句不统一，尽管第四句会成为另一主题句(Many Pakistanis speak English)很好的推展句。第五句说服力不强。

当然，在写成段落时，没有必要在每个句子开头写上 "because"，但是，在动笔展开句子时，头脑里要想着这个词，这种检验方法能帮助你把注意力集中在某个重心，围绕主题思想层层展开。

上面我们讨论了主要推展句的一种展开方法。而展开次要推展句的方法与主要推展句类似，这里我们就不再复述了。

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