Respuesta:
1. I fell down while I was going down the stairs.
2. He was driving very fast when he had the accident.
3. It was snowing when we left home.
4. I didn't answer your call because I was working.
5. This morning, I got up and made breakfast for everybody.
6. When I saw her, she was wearing a really nice purple dress.
7. Last Saturday we got up late and missed the train.
8. I didn't say hello because you were walking very fast.
9. I was sleeping happily when a loud noise woke me up.
10. What were you doing when I called you last night?