A prisoner's dilemma game is played for a fixed number of periods. The fully rational solution for each player is to defect (confess) in each period. However, in experiments with students, players often cooperate for a significant number of periods if the total number of repetitions is fairly large (such as 10 or 20). What explanation can you give for this behavior? Students may cooperate in experiments such as a multi-period prisoner's dilemma because A. they believe in fairness. B. the game is played for an unknown number of periods. C. they take the game too seriously. D. they are rational. E. the game is not played indefinitely.