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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：I dont teach because teaching is easy for me. Teaching is the most difficult of the various ways I have attempted to earn my living: mechanic, carpenter, writer. For me, teaching is a red-eye, sweaty-palm, sinking-stomach profession. Red-eye, because I never feel ready to teach no matter how late I stay up preparing. Sweaty-palm, because Im always nervous before I enter the classroom, sure that I will be found out for the fool that I am. 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基本可以遵循下面的三部分规则。 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。 | 
