How does a monopolistically competitive industry differ from an oligopoly industry?

a. Monopolistically competitive industries set price equal to marginal cost; oligopoly industries set price equal to output.

b. Monopolistically competitive firms compete with each other; oligopoly firms cooperate with each other.

c. Monopolistic competition has many small firms; oligopoly has a few large firms.

d. Monopolistically competitive firms earn profit in the long run; oligopoly firms earn losses in the long run.