有些词只要出现句子中，就表示这个句子是过去时，常见的标志性词语有：yesterday , last , ago , before , in+年或月 , on+日 , just now(或者a moment ago) ；再加上was+v-ing，就可以判断这个句子是过去进行时了。例如：
1.I called you yesterday afternoon but there was no answer.
昨天下午我打电话给你，但是没有人接电话。
2.I was visiting a friend of mine most of the afternoon.
我昨天下午大部分时间，都在一个朋友家里。
3.It was raining hard when I left my office.
当我离开办公室时，雨下得正大。
4. When you called，I was eating.
你打电话时，我正在吃饭。
5. When I was cleaning the windows， my brother was sweeping the floor.
我在擦窗户的时候，我弟弟在拖地。
6. Some students were playing football，while others were running round the track.
一些学生在踢足球，同时别的学生正在跑道上跑步。
7. We were walking along the river when（suddenly） It rained.
我们沿着河边散步，突然下起雨来。
8. They were watching TV when the lights went out.
停电时，他们刚好在看电视
9. She went to see Xiao Li. He was leaving early the next morning.
她去看小李。他第二天一早就要离开此地了。
10. She asked him whether he was coming back to lunch.
她问他晚饭是否准备回来吃。