Which one of the following correctly identifies a characteristic of a monopolistic market?

There is no excess capacity in a monopoly.
A monopolist maximizes profit at the point where price = marginal cost.
A monopolist will always earn supernormal profits.Correct
A monopoly firm faces a perfectly elastic demand curve.

Explanation
Unlike perfect competition, monopolies can expect to earn supernormal profits in both the short and long run due to barriers to the entry of new firms.