核心规则
过去进行时由 was/were + doing 构成，把动作放在过去某一时刻或时段内部观察。它常提供背景，一般过去时则常叙述进入故事主线的完整事件。
结构与例句
At eight last night, we were reviewing the data。When the lights went out, the team was working。While I was cooking, my sister was setting the table。
| 关系 | 常见搭配 |
|---|---|
| 长过程被短动作打断 | was/were doing + when + did |
| 两个过程同时进行 | while + was/were doing, was/were doing |
| 礼貌而试探的表达 | I was wondering if... |
使用场景
叙事中，过去进行时搭建时间背景，一般过去时推动事件发展。它还可表示未完成的临时过程或过去一段时间的变化。
常见错误
错误： When I was arriving, he called. → arrive 是短暂完成事件，通常写 When I arrived, he called。
错误： They were discussed the issue. → 正确： They were discussing the issue。
易混知识点
过去进行时关注过程，过去完成时强调某过去节点之前已经完成：I was reading when she arrived；I had finished reading before she arrived。
总结
先设定过去参照点，再判断要呈现的是当时展开的过程还是已经完成的事件。
高中 · 过去背景与动作交叉
高中学习重点
when 可引导较短事件，也可指时间段，不能机械地规定时态；while 更突出两个过程重叠，后面常用进行时。was/were about to do ... when ... 表示“正要做某事，这时……”，was/were doing ... when ... 表示“正在做某事，这时……”。
过去进行时还可以让请求更委婉：I was hoping you could help。这里不强调动作真的持续，而是拉开语气距离。
小练习
- 填空：I ___ (walk) home when it suddenly ___ (start) to rain.
- 填空：While the teacher ___ (explain), the students ___ (take) notes.
- 补全：We were about to leave ___ the phone rang.
参考答案
was walking; started。was explaining; were taking。when。