The naturalist Charles Darwin, who is credited with developing the theory of evolution by natural selection, suggested that adaptations of organisms were the result of

A. their genetic structure, which is indicated by internal genetic codes.
B. how much sunlight an organism is exposed to.
C. adaptations to different environmental conditions.
D. how much activity an organism has, including the amount of time it spends sleeping.
E. the number of years of an organism's existence.