I had this question as well and if you look closely, the question describes the function in terms of rabbits, when the actual question describes fish. I believe that because the question is asking for fish when only information on rabbits has been given, the only logical answer would be e. none of the above...
x is the hypotenuse so it means the other ones that are adjacent and opposite and you're looking for the hypotenuse so you can do c Square equals to a square + b square