英语中的if条件句由两部分组成,一个是连词if引导的条件状语从句,一个是表示结果的主句,if从句可置于主句之前或之后。主从句的谓语动词的时态形式取决于说话者认为结果是否是真实的。if条件句分为零条件句、第一条件句、第二条件句和第三条件句四种,见下表（The 4Types of Conditionals）：
请同学们先看下面教材里的典型句子,认真体会斜体部分的用法:1.In the past,if someone like me had failed to get into university through the college exam,he would have had no chance of getting a degree.(北师大版教材模块五Unit15 Lesson1 P36)2.I know that I wasn’t a willing student and I shouldn’t have been so difficult at school,but
请同学们先看下面教材里的典型句子，注意斜体部分的比较级用法：
1. It＇s no pleasure looking through these any longer because nature is one thing that really must beexperienced.（人教课标版教材模块一Unit1 P2）
