Fact 1: Fish have a centralized nervous system with a brain. Fact 2: Vertebrates have the most defined and developed nervous system. Given the two facts above, what are vertebrates?

Pick your answer from:
(a). voles;
(b). pigs;
(c). otters;
(d). fish;
(e). toads;
(f). koalas;
(g). Birds;
(h). humans;
The answer is:
(d).