When or while?

1. The students were doing an exercise ... the bell rang.

2. I saw an accident ... I was waiting for my friend at the bus stop.

3. ... she was reading an email, the computer turned off.

4. He fell down ... he was climbing a tree.

5. ... my mum came home, my sister was doing her homework.

6. We found some old photos ... we were tidying our room.

7. ... you called me last night, I was sleeping.

8. Jack broke his arm ... he was skiing.

9. ... the fire alarm went off, we were listening to music.

10. She started to cry ... she was watching a movie.