基本信息
第一部分 篇章结构
一、科普类文章
1．引出中心内容的方法
(1)A but B。
这个时候B是文章的中心。为了不让文章显得太突兀，一般会先讲A，即普通的内容(科普类文章一般介绍的是我们不太熟悉的内容)。另外，A也有可能是一种欲扬先抑的写作手法，与B的意思正好相反。
Most animals have little connection with animals of a different kind, unless they hunt them for food. Sometimes, however, two kinds of animals come together in a partnership (伙伴关系) which does good to both of them. You may have noticed some birds sitting on the backs of sheep. This is not because they want a ride, but because they find easy food in the parasites (寄生虫) on sheep. The sheep allow the birds to do so because they remove the cause of discomfort. So although they can manage without each other, they do better together.
