Monopolies are inefficient because, at the profit-maximizing output level, (a) MC = MR (b) MC does not equal MR (c) MB = MC (d) P does not equal MC (e) P = ATC

The answer is (d) P does not equal MC .

In a perfectly competitive market, price (P) equals the marginal cost (MC) at the profit-maximizing level of output. However, in the case of a monopoly, profit is maximized when the marginal revenue (MR) equals marginal cost. This is because the demand curve in monopolies is downward sloping, so changes in quantity have an impact on the price. The demand curve for a perfectly competitive firm is horizontal, so it can sell every other good at the same price.