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.
2.I was visiting a friend of mine most of the afternoon.
3.It was raining hard when I left my office.
4. When you called，I was eating.
5. When I was cleaning the windows， my brother was sweeping the floor.
6. Some students were playing football，while others were running round the track.
7. We were walking along the river when（suddenly） It rained.
8. They were watching TV when the lights went out.
9. She went to see Xiao Li. He was leaving early the next morning.
10. She asked him whether he was coming back to lunch.