When I went downstairs , they were already eating breakfast .
When I got up this morning , it was snowing .
While I was driving here , I was thinking about you .
While you were talking to her , I was reading a magazine .
While the guide was lecturing about the Roman ruins , some of the tourists were resting their feet in the cafe across the road .
They were building a dam last winter .
2. 过去进行时用在时间或者条件分句中表示过去将来正进行的动作。
He promised not to mention this when he was talking to her .
He told me to wake him up if he was sleeping .
3. 在口语或者记叙文中可以用过去进行时表示的持续动作作为背景，以引出由一般过去时表示的新动作。
While I was preparing a speech , my secretary entered my office .
The accident happened while I was working in the garden .
We were doing our homework when the teacher stepped in .
We were doing our homework when the light went out .
One morning the three sisters were together in the drawing room . Mary was sewing . Lucy was playing the piano , and Jane was doing nothing ; then suddenly the door opened and John burst in .
4. 过去进行时与 always , forever , constantly 连用表示羡慕、讨厌、赞扬、不满等感情色彩。
He was always changing his mind .
5. 过去进行时表示按计划安排过去某时将发生的动作。
They were leaving a few days later .
6. 动词 hope , want , wonder 的过去进行时用来提出请求，表达婉转的口气。实际上表示的时现在的情况，虽然一般过去时、现在进行时也可以表达委婉的语气，但都不如过去进行时那样婉转。
I was hoping you could send me some monkey stamps .
I was wondering if you could help me .
7. 过去进行时在某些结构中作想象性用法，表示与现在事实相反，或表示将来的臆想情况。
If they were leaving tonight , I\'d like to go with them . 若今晚他们要走，我很想一块走。
I wish they were not speaking so loudly . 但愿他们不大声喧哗。
8. 有时用 come , go , plan , expect , hope , intend , look forward to 等的过去进行时表达本来打算而实际没有做成的事情。
He was expecting to finish the work last month , but unexpectedly the machines went out of order . 他原想上个月做完这件工作，但不巧机器出了故障。（= had expected）
I was going to the cinema tonight , but the manager told us to attend a meeting . 今晚我本想去看电影，但经理告诉我要去参加一个会。
9. 过去进行时还可以表示该动作还未结束或已进入一个新阶段。
By the time he was ten , Edison was already doing experiment in chemistry . 到十岁时，爱迪生已经在做化学实验了。
Soon all the people of the city were talking of the wonderful cloth . 很快全城的人都在谈论这种神奇的布。
10. 在口语中，过去进行时有时既不是表示某时某刻正在进行的动作，也不是表示婉转口气或铺叙背景，而只是说明最近过去的事情。
I was asking what you thought of it . 我是问你是怎么想的 。
I was hearing John had got a new job . 我听说约翰有了新工作。
11. “过去进行时”与“一般过去时”的区别在于，前者主要描述一个持续性的动作，而后者表示一个完成的动作。对比：
They were building a dam last winter . (指在建造中)
They built a dam last winter . (指造好了)
12. 使用过去进行时应注意，有些瞬间动词（accept , allow , admit , complete , decide , end , give , receive , refuse , permit , promise , break , fall , slip , stop , marry , …）没有进行时，开始的时间就是结束的时间。