<正> Unit 3 Why Do We Believe thatthe Earth is Round重点及疑难攻破:1.preface:n.开端,开始。例如:(1)An informal brunch served as a preface tothe three-day conference.以一顿非正式的早午餐作为三天会议的开端。(2)He prefaced his speech with an amusingstory.他用一则有趣的故事开始了他的演说。2.cite:v.举出,引用。例如: