1）在确定的过去时间里所发生的动作或存在的状态。
时间状语有：yesterday, last week, an hour ago, the other day, in 1982等。
when, after, as soon as 引导的时间状语从句，表示主句动作开始的时间。
Where did you go just now?
2）表示在过去一段时间内，经常性或习惯性的动作。
When I was a child, I often played football in the street.
Whenever the Browns went during their visit, they were given a warm welcome.
