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。