In a Prisoner's Dilemma, Two Prisoners Have Agreed with Each

In a prisoner's dilemma, two prisoners have agreed with each other that they will not confess. Now each of them is offered a deal: "If you confess, we will punish your friend harshly but let you off easy." The probability that they will both cooperate with each other (instead of confessing) is increased if they

A) are in constant communication with each other.
B) have promised each other not to confess.
C) both have a high self-monitoring personality.
D) realize that they both go to prison if both confess.