Which statement BEST describes the theory of natural selection?

a. It increases the size of a population

b. it happens over a long period of time.

c. It guarantees the survival of a species.

d. It requires the individuals to be identical

C, it guarantees the survival of a species, for example there are a species of moth called the pepper moth, some of them are light and some of them are dark, where the pepper moths live has dark trees, the pepper moths that are lighter in color are likely to be eaten by birds because they are easier to see making the amount of light pepper moths scarce while the dark pepper moths live to breed and have offspring.