Marginal Revenue Is Less Than Price for a Single-Price Monopolist

Marginal revenue is less than price for a single-price monopolist because the

A) firm's output decisions do not affect the selling price.
B) firm must lower its price for all units if it wants to sell more of the product.
C) monopolist charges a price higher than the unit production cost.
D) monopolist must worry about how its price setting will lead to entry by other firms.
E) monopolist has achieved economies of scale.