三．一般过去时。定义动词的过去式：
1．表示过去某个特定时间或某一段时间发生的动作或情况。
►. We visited the school last spring.
►. I went to school by bike when I was in middle school.
►.
2．在表示时间或条件等的状语从句中代替过去将来时。（参）
►. She told me that she would not go with us if it rained the next day.
►. They would not leave until she came back.
►. My friend promised to marry me once she made her final decision.
3．一般过去时，现在时和过去时的几组差异：（别以为这很简单，下面的差异你不一定明白。）
● Her brother was a chemist.（已去世）
● Her brother is a chemist.（尚健在）
● That's all I had to say.（话已说完）
● That's all I have to say.（言之未尽）