The simplest prisoners’ dilemma is a game that, in part, requires
a) two players who are able to communicate with each other.
b) two players who are unable to communicate with each other.
c) monopolistic competition.
d) an oligopoly with one very large firm.

Answer to your question is: B) Two players who are unable to communicate with each other.

Explanation:

Prisoner's dilemma is a scenario in which two completely rational individuals/companies might not cooperate, even if it appears that it is in their best interests to do so.

For the Prisoner's dilemma to be true, both persons/companies should not be able to communicate with each other otherwise they will collude and reach mutual best interest.

Other option explanation:

So your option A is totally against the assumption of Prisoner's dilemma.

Option C says Monopolistic competition. In case of Prisoner's dilemma there are 2 equal players and no monopoly so this option is also not correct

Option D says oligopoly with one very large firm. This is also wrong as Oligopoly with one very large firm will have several smaller other players and Prisoner's dilemma work between only 2 players.

i have economics during second block which is easy to me. anyways, i think b.