The Dilemma in a Prisoner's Dilemma Is That

The dilemma in a prisoner's dilemma is that:

A) the outcome is random, so players are uncertain about which strategy to play.
B) only one player has a dominant strategy, but the other player is uncertain about what to do.
C) the players would be better off if they both played a dominated strategy.
D) the players may be trapped in a game they don't know how to play.