1. They were drinking tea when I came home.
2. He was walking along the river when a boat was passing
3. The old man was thinking about his plan when he fell asleep.
4. We listened to an interesting lecture yesterday.
5. When I entered the classroom, the teacher was writing words on the blackboard and the pupils were coping them into their exercise-books.
6. They were getting ready to go out when it began raining.
7. Yesterday at one o'clock I was having lunch at the canteen.
8. When he came in, I was doing my exercises.
9. What were you doing at eight o'clock yesterday?
10. At this time yesterday I was going home.
11. You were sleeping when I went out.
12. He was reading on the sofa when I came in and sat down beside him.
13. I was walking along the street with my friend when a tram passed.
14. She looked out of the window when I saw her.
15. We were answering the teacher's questions when the headmistress entered the classroom.