One of the Differences Between Perfect Competition and Oligopoly Is

One of the differences between perfect competition and oligopoly is:

A) that an oligopolist rarely earns economic profit, whereas a perfectly competitive firm will always earn economic profit.
B) that perfectly competitive firms often engage in non-price competition, whereas oligopolists don't.
C) that while a perfectly competitive firm earns zero economic profit in the long run, the oligopolist can earn positive economic profit in the long run.
D) that a perfectly competitive firm will advertise while an oligopolist will not advertise.