Found the answer. Hope it could help someone.
24.Almost all animals (that hibernate) prepare for (it) during summer (by eating) large amounts of food, (which they convert) to thick layers of fat.
Why? isn't it referring to hibernate?
because "hibernate" isn't a noun, a "thing." The sentence would be correct if it read something like this: "Almost all animals that go into hibernation prepare for it. . . ."