It can be rational to play tit-for-tat in a repeated Prisoners’ Dilemm

It can be rational to play tit-for-tat in a repeated Prisoners’ Dilemma game

A) only if the game is played an infinite number of times.
B) if the game is played an infinite number of times, or if it is uncertain how many times it will be played.
C) only if the game is played a finite number of times, and that number is known by all the players in advance.
D) for n-1 of the n periods it will be played, if n is known in advance.
E) at no time; tit-for-tat is an irrational strategy in this situation.

ANSWER

B