Here are the correct answers for the exercises based on degrees of comparison:
1. 3. more difficult
2. 2. funnier
3. 3. best
4. 4. worst
5. 1. best
6. 4. better
7. 1. the best
8. 3. the better
9. 3. most difficult
10. 1. noisier
11. 3. the best
12. 3. uglier
13. 4. the best
14. 4. the most interesting
15. 4. healthier
16. 3. worst
17. 4. bigger
18. 3. more polite
19. 4. the widest
20. 2. nicer.