Answer:
d. the oligopolists earn the highest profit when they cooperate and behave like a monopolist.
Explanation:
An oligopoly is when there are few large firms operating in an industry.
When oligopoly firms come together and agree to set a price, they are known as cartels and are acting as a monopoly. Firms in a cartel earn the highest profit because they act as a monopoly compared to when they aren't in a cartel and each firm sets their own prices to maximise profit. In a case where firms in an oligopoly do not form a cartel, they engage in price wars and other forms of competition which might make firms earn lower profits compared to when they are in a cartel.
Collusive agreements aren't always binding. Firms might have incentives to cheat on the agreement if the payoff from cheating is higher than not cheating.
I hope my answer helps you.
