At the End of the Cold War Period,the Prisoner's Dilemma

At the end of the Cold War period,the prisoner's dilemma model was no longer the best way to describe the superpower arms race because

A) the entire nuclear arsenals in both countries were under the control of disarmament agreements.
B) both countries realized that China's nuclear arsenal was a bigger threat.
C) the United States' preference ordering changed,and its preferred choice was something other than unilateral armament.
D) hydrogen bombs made all other weapons obsolete.