Refers to the ability of an individual to survive and reproduce, whereas is any inherited characteristic that increases one’s chance of survival.
a. adaptation . . fitness
b. natural selection . . fitness
c. fitness . . adaptation
d. adaptation . . natural selection

The answer would be : c. Fitness . . .adaptation

An organism's physical fitness really played a major role on its capability to survive in the environment.
After a prolonged period of time, its off spring will inherited some sort of characteristic that make them more capable of surviving in a secific environment