Past Simple\ Past Continuous.1.They (to drink) tea when I (to come) home.2. He (to walk) along the river when a boat (to pass).3. The old man (to think) about his plan when he (to fall) asleep.4. We (to listen) to an interesting lecture yesterday.5. When I (to enter) the classroom, the teacher (to write) words on the blackboard adn the pupils (to copy) them into their exercise - books.6. They (to get) ready to go out when it (to begin) raining.7. Yesterday at one o'clock I (to have) lunch at the canteen.8. When he (to come) in, I (to do) my exercises.9. What you (to do) at eight o'clock yesterday?10. At this time yesterday I (to go) home.

They were drinking tea when I came home.
(Здесь используется Past Continuous для действия, происходившего в момент другого действия в прошлом, и Past Simple для действия, которое произошло после.)

He was walking along the river when a boat passed.
(Again, Past Continuous для длительного действия в прошлом и Past Simple для краткого события, которое прервало действие.)

The old man was thinking about his plan when he fell asleep.
(Здесь также Past Continuous для действия, которое длилось, и Past Simple для события, которое произошло неожиданно.)

We listened to an interesting lecture yesterday.
(Past Simple, так как это завершённое действие в прошлом.)

When I entered the classroom, the teacher was writing words on the blackboard and the pupils were copying them into their exercise books.
(Past Simple для действия, произошедшего первым, и Past Continuous для действий, происходивших в момент, когда произошло другое событие.)

They were getting ready to go out when it began raining.
(Past Continuous для действия, которое происходило в момент другого события, и Past Simple для действия, которое прервало действие.)

Yesterday at one o'clock I was having lunch at the canteen.
(Past Continuous для описания действия, происходившего в определённый момент в прошлом.)

When he came in, I was doing my exercises.
(Past Simple для события, произошедшего первым, и Past Continuous для действия, которое продолжалось.)

What were you doing at eight o'clock yesterday?
(Past Continuous, так как это вопрос о процессе, который происходил в момент времени.)

At this time yesterday I was going home.
(Past Continuous для описания действия, происходившего в определённый момент в прошлом.)