Final answer:
A firm with market power in pricing faces a downward sloping demand curve, as opposed to a flat demand curve, which is characteristic of perfectly competitive firms.
The correct option is D. a downward sloping demand curve.
Step-by-step explanation:
A firm with market power in pricing does not face a flat demand curve as that is a characteristic of a perfectly competitive firm. Rather, such a firm actually faces a downward sloping demand curve.
This means that if the firm decides to charge a high price, it can only sell a lower quantity of goods, and if it sets a lower price, it can sell a higher quantity. This is akin to the demand curve faced by a monopolist, which is the same as the market demand curve and is characterized by its downward slope.
Therefore, the correct option for a firm with market power in pricing is (d) a downward sloping demand curve.