task 2.
1.happened
2. was walking
3. was talking
4.slipped
5. fell
task3
1.we were going down the lift when it suddenly stopped
2. what were they doing while you were fixing your bike?
3. when the doorbell rang, I got up, went to the door and answered it
4.when I opened the box, I saw a cute little kitten
5. while he was eating a chocolate bar, he broke a tooth
task 4
1. .... when the telephone rang
2. .... while his mother was cooking dinner
3.... and this noise came from the kitchen
4. ...at 6 p.m. I was doing my homework
5..... the pupils were running around the classroom