Because Each Oligopolist Cares About Its Own Profit Rather Than

Because each oligopolist cares about its own profit rather than the collective profit of all the oligopolists together,

A) they are unable to maintain the same degree of monopoly power achieved by a monopolist.
B) each firm's profit always ends up being zero.
C) competitive pressures are absent from the market.
D) it will be easier to maintain collusive agreements.