Which of the Following Is True of Game Theory

Which of the following is true of game theory?

A) Cooperation is more likely to occur in repeated games than in one-shot games.
B) At a Nash equilibrium, all firms have an incentive to change behavior.
C) Cooperative strategies are equally likely in one-shot and repeated games.
D) A tit-for-tat strategy is a way to reward noncooperation and punish cooperation in a repeated game.
E) Collusion is an example of a noncooperative game.