16. The profit-maximization problem for a monopolist differs from that of a competitive firm in which of the following ways? (A)A competitive firm maximizes profit at the point where average revenue equals marginal cost； a monopolist maximizes profit at the point where average revenue exceeds marginal cost. (B)A competitive firm maximizes profit at the point where marginal revenue equals marginal cost； a monopolist maximizes profit at the point where marginal revenue exceeds marginal cost. (C)For a competitive firm, marginal revenue at the profit-maximizing level of output is equal to marginal revenue at all other levels of output； for a monopolist, marginal revenue at the profit- maximizing level of output is smaller than it is for larger levels of output. (D)For a profit-maximizing competitive firm, thinking at the margin is much more important than it is for a profit-maximizing monopolist.