This is a right triangle so we can use the Pythagorean Theorem to answer. The hypotenuse will always be C and the longest side and then A or B can be any of the legs. As you can see I tested out each of the options to figure out which one would be the best answer. You can see the process in the pictures. I color coded each section so that you have an idea of what each looks like when worked out. Let me know if you need more clarification! :)