Concept:In a perfectly competitive market, the firm is a price taker.
Explanation:The average revenue (AR) is the price per unit sold.
In a perfect market, the price is fixed and constant for the firm.
Therefore, the AR curve is a horizontal straight line at the market price.
This horizontal price line is exactly the demand curve faced by the firm.
Thus, the average revenue curve coincides with the firm's demand curve.
Answer:C. demand curve of the firm