Presently, there are several subspecies of beach mice on each of the different of the barrier islands in Florida and Alabama. Each subspecies has a slightly different fur color. What caused the population of mice to become distinct subspecies distributed on the various barrier islands?

a. Different lines of beach mice developed different fur color for each island because they needed that fur color in order to avoid the predators on that island.
b. The mice were quite variable and those whose features were best suited to avoid predators on each island reproduced most successfully.
c. All mice are essentially alike and there are not really different subspecies on the different islands.
d. There are different predators on different islands and for that reason, individual mice on each island gradually developed the fur color that they needed in order to survive on that island.