In a Repeated Prisoners' Dilemma Decision,both Managers Can Make Credible

In a repeated prisoners' dilemma decision,both managers can make credible threats to punish cheating because

A) if either manager cheats,the other manager can increase its profit by also cheating.
B) both of the cheating cells in the payoff table are strategically stable cells.

C) when both firms cheat,they both avoid the Nash equilibrium cell.
D) both a and C