A Monopolist Can Sell Nine Units at $10 Per Unit

A monopolist can sell nine units at $10 per unit.Since he can sell ten units if he lowers his price to $9 per unit,we know that the

A) marginal revenue of the monopolist is $0.
B) monopolist should sell no more than nine units.
C) monopolist should be raising price above $10 per unit.
D) monopolist is making a loss if he lowers his price.
E) monopolist is maximizing his profit.