1. Fred was sleeping
2. Jack was putting on, the telephone rang
3. While Andrew was writing, his helper was taking pictures (while - это не when. Он указывает на то, что два продолжительных действия проходили одновременно)
4. When mum opened, she saw Greg who was cleaning
5. Jack was doing his homework
6. What did Debbie write
7. Someone came to visit, I saw
8. It was snowing, I was waiting
9. It began to snow when we reached
10. What were you doing