A firm in monopolistic competition maximizes its profit by ________.
A. Differentiating its good and producing the quantity at which price equals marginal revenue
B. Producing the quantity at which marginal revenue equals marginal cost and then adding a markup
C. Raising its price and producing so that it always has excess capacity
D. Producing the quantity at which marginal cost equals marginal revenue and charging the highest price at which it can sell that quantity