2)
1. i was writing a letter, when the light went out.
2. when we arrived the lesson had already started.
3. you looked very busy when i was asking you at night. what did you do?
4. we shared a flat her when we were students. she always complained about my untidiness.
5. they saw helen at the party. she wore a beautiful dress.
3)
1. i found the toy, which i had lost.
2. my sister had spoke about places she visited.
3. they had wanted to see you yesterday.
4. we had completed all the preparations for the trip by 5 o'clock
5. he found the girl even more beautiful then he had expected her to be.