过去进行时 Past Progressive
形式：was 或 were 尾随-ing。
意义：1，显示某一状态或某一动作在进行中。
如：
It was raining when the doctor left his house.
医生在下雨的时候出门。“下雨”曾持续一段时间，覆盖了医生出门这个一过性动作。
2，两个动作在同时进行中。
I was mending the TV while she was reading.
3，单一动词。
I was having breakfast at 8 o'clock this morning. |
