The Pure Monopolist Who Is Nondiscriminating Must Decrease Price on All

The pure monopolist who is nondiscriminating must decrease price on all units of a product sold in order to sell additional units.This explains why:

A) there are barriers to entry in pure monopoly.
B) a monopoly has a perfectly elastic demand curve.
C) marginal revenue is less than average revenue at all levels of output.
D) total revenues are greater than total costs at the profit-maximizing level of output.