Which of the Following Is True of Game Theory

Which of the following is true of game theory?

A) A dominant strategy in a non-cooperative game yields the same result as that in a cooperative game.
B) A tit-for-tat strategy is a way to reward noncooperation and punish cooperation in a repeated game.
C) At a Nash equilibrium, all firms have an incentive to change behavior.
D) A tit-for-tat strategy is the most effective strategy to promote cooperation.
E) Collusion is an example of a noncooperative game.