Which of the Following Statements Illustrates the Free-Rider Problem

Multiple Choice

Which of the following statements illustrates the free-rider problem?

A) By reliably reciprocating a cooperative behavior, all individuals in the population increase their fitness.
B) Some daughters forego having offspring of their own as they help their mother with brood care.
C) An individual spends only half an hour grooming others for each hour of grooming it has received.
D) Some individuals forgo reproduction to avoid overpopulation of a species' habitat.