Which of the following is an example of adaptation?

a) A rabbit population in which all of the members change fur color from brown to white as the seasons change

b) A butterfly population where each individual makes more of an enzyme for processing toxins as its exposure to toxic plants increases

c) An eagle population where adult eagles develop a tolerance for invasive mites over five years

d) A fish population in which the average skin brightness decreases over several generations in the presence of predators