A) surely isn't a hypothesis that could be used to assess the question "does sunlight or temperature of the rabbit's habitat affect fur thickness" because it doesn't talk about fur thickness.
B) could be a hypothesis. However, hypothesis usually are not stated in if-then clauses. However, it also does contain an idea with a possible consequence.
C) is the correct answer. This idea predicts that rabbits in warm habitats will have dark fur. This is how hypothesis are usually stated.
