Which of the following describes natural selection? a. a population of mammals lives near the water, water levels rise and the habitat becomes swampy, the animals have trouble moving in the water, the population changes to a shorter-legged type so they can move more easily in the water b. a population of mammals lives near the water, water levels rise and the habitat becomes swampy, the act of swimming shortens the legs of the mammals, the offspring of the mammals have shorter legs c. water levels rise and a habitat becomes swampy, a population on high ground observes the change, individuals with shorter legs migrate to the area d. a population of mammals varies in the length of their legs, water levels rise and the habitat becomes swampy, the individuals with shorter legs are better able to swim to food, the population evolves to become shorter-legged 1 points