PERIOD 15
1. had known/ would have gone
2. hadn't been
3. returned
4. didn't invite
5. would you do/ were
6. would come
7. rang
8. were
9. were
10. had
11. would feel
12. offered
PERIOD 16:
1. Would have bought
2. would have seen/ had gone
3. had had
4. had been/ would have visited
5. would have fed
6. didn't rain
7. would have written
8. had played/ would have won
9. did
10. had known
11. had had
12. had been
PERIOD 17:
4. rings
5. were
6. is
7. were
8. had been
9. had
10. hadn't had
11. had driven
12. didn't read