Answer:
C. Under particular circumstances that persisted for long periods, each of these structures presented greater costs than benefits
Explanation:
Natural selection is evolutionary mechanism which favors traits (structures, behavior) of an organism that help him survive and reproduce. But, when there are some structures of an organism that are useless, selective pressure acts against them. Structures that don't contribute to an organism’s survival and reproduction, but are not directly harmful will take long time to be eliminated.