The answer is A: Swimming into colder water. When fish are hot, they swim deeper; which is the same thing as swimming into cold water. B is incorrect, because if the fish is hot, there's no use going to the surface-which is hotter- to evaporate water from it's skin. By the way, what's the use of evaporating water again? The fish is still hot! C is wrong, because the only fish known to man that expels water, is the puffer-fish. Since the answer talks about fish in general, C is eliminated too. Finally, D is wrong because... um... someone please explain to me why a fish will speed up when the fishes temperature is getting hotter then supposed to!
Hope I helped!