learning aims: 1. to learn some information about hiv/aids. 2. to learn some important words and expressions. important point: to grasp some important and useful words, expressions and sentence patterns. difficult point: to improve the skills of reading. 使用说明及学法指导：1. 通过阅读课本p 及查阅unit 3单词表和字典，完成预习案。2. 完成时间：20分钟。预习案 previewing case task 1 read the text to find out the following phrases and words. 1.引起疾病______________ 2. 流感病毒______________ 3.减弱/破坏人的免疫系统________________
