Why does cooperative behavior break down in games with finite endpoints?

A) Each player has an incentive to deviate from a cooperative strategy during the last period.
B) A Nash equilibrium in pure strategies is not possible in finite repeated games.
C) Finite games have the same outcomes as one-period games, and cooperation is not possible in one-period games.
D) A Nash equilibrium is only possible in mixed strategies in finite repeated games, but all of the probabilities assigned to particular strategies approach zero as the number of finite game periods becomes large. Thus, we cannot evaluate the expected payoffs in these games.

A