Ответ:

1. We were playing chess,when Carl's mother phoned.

2. While all my friends were enjoying themselves, I was studying for an exam.

3. Why were you making all that noise,while I was trying to sleep?

4. When I got home on Saturday night, my parents were watching the film on TV.

5. Maggie was getting ready to leave, when I called her.

6. The students didn't pay attention ,when the teacher was explaining the exercise.

7. As I was doing the shopping, I saw Kathy.

8. Did they visit the Prado Museum when they went to Spain?

9. As soon as I tasted the food, I realized that it was too salty.