Market structure has implications for a firm's profitability. Which of the following statements is true? A. An oligopolistic firm, since it faces competition, takes the market price as given. B. All firms maximize profits by producing at the quantity where marginal revenue equals marginal cost. C. Because it possesses significant market power, a competitive firm will always earn positive economic profits in the long-run. D. A monopolist maximizes profit by producing at the quantity where marginal revenue equals marginal cost, but a competitive firm, being a price taker, must maximize revenue