I.
1. arrived, had started
2. was having
3. were doing
4. came, had decorated, had baked, had bought
5. was making, went
II.
1/ were singing, came
2. was giving, walked
3. blew, was crossing
4. was doing, was playing
5. was singing, was cooking
6. was raining, went
Past Continuous (was/were + гл. с окончанием -ing) используем для действий, которые происходили в какой-то момент в прошлом.
III.
1. got, had started
2. landed, was setting
3. felt, had eaten
4. had finished, came
5. had spent, asked
6. gave, had corrected
7. entered, had rung
Если действие произошло раньше другого, используем Past Perfect (had + 3ф.гл)