Which of the Following Best Explains Why the Monopolist's Marginal

Which of the following best explains why the monopolist's marginal revenue is less than the sales price?

A) To sell more units, the monopolist must reduce price on all units sold.
B) As the monopolist expands output, the average total cost will decline.
C) The monopolist charges each consumer the highest possible price.
D) When a firm has a monopoly, consumers have no choice other than to pay the price set by the monopolist.