过去进行时表示过去某一时刻或某一段时间内正在进行的动作或状态。其构成是“主语 + was/were + 现在分词（动词 -ing形式）”。例如：

1. I was watching TV at 9 o'clock last night.

2. They were playing football all afternoon.

3. At 8 o'clock last night, I was watching TV.

4. When I got to the top, he was reading.