1. before 和after
before引导时间状语从句，往往表示主句的动作先于从句的动作发生，翻译形式多种多样：
“......才”；“......就”；“还没来得及......就......”;"趁着......"。
We had sailed four days and nights before we saw the land.(......才)
We hadn't run a mile before Tom felt tired.(......就)
Before I could say a word, he had handed the paper in.(还没来得及......,就......)
Please write it down before you forget it.(趁着......)
