Ответ:
When Kate returned, I was listening to the radio.
When we were doing our project, my sister entered the room.
When my mother came home, I was having dinner.
What were they doing when you saw them?
The young people were dancing when the parents returned home.
They were disscussing the latest news when the telephone rang.
When he was washing the dishes, he broke a plate.
When we were doing our project, my sister entered the room.
My friend was playing with his cat when I came to see him.
When my sister came in, I was doing my homework.