12.3
1. The phone rang when I was having a shower.
2. It began to rain when I was walking home.
3. We saw an accident when we were waiting for the bus.
12.4
1. fell............was painting
2. was reading........heard
3. Were you watching.......
4. was waiting..........arrived
5. wasn't driving......happened
6. broke........was doing
7. took.........wasn't looking
8. didn't go (у них опечатка- вместо you должно быть not).......was raining
9. were you doing
10. saw.......was wearing(не очень уверена в этом)