Jawaban:

a) The comparative forms of the adjectives are:

1. Ann is happier than her sister.
2. My hair is longer than my sister's hair.
3. These exams are getting worse every year.
4. John is thinner than Bob
5. The sooner, the better.

b) The superlative forms of the adjectives are:

1. I am the tallest in the class.
2. This is the most expensive hotel I've stayed in.
3. New York is one of the busiest streets in the USA.
4. Jack is the best football player.
5. North Pole is the coldest place on Earth. (Note: "coldest" is already in the superlative form)

c) The comparative or superlative forms of the adjectives are:

1. My brother is younger than me. (comparative)
2. Many people want to be richer. (comparative)
3. Today's weather is worse than yesterday's. (comparative)
4. She is probably the angriest person I know. (superlative)
5. His biggest desire is to return home. (superlative)