Suppose perfectly competitive market conditions are characterized by the following inverse demand and inverse supply functions: P = 100 - 5Q and P = 10 + 5Q. The demand curve facing an individual firm operating in this market is:
A. P = 100 - 5Q.
B. a horizontal line at $9.
C. a horizontal line at $55.
D. P/N = (100 - 5Q)/N, where N is the total number of firms in the competitive market.