Ответ:
I
1. is
2. are
3. are
4. am
5. is
II
1. short - shorter - the shortest
2. big- bigger- the biggest
3. bad-worse-the worst
4. clever- cleverer = the cleverest
5. funny - funnier - the funniest
6. difficult- more difficult- the most difficult
III
1. was
2. were
3. was
4. was
5. were