Answer:
The answer is D.
Explanation:
The demand curve faced by perfectly competitive firm is horizontal. This means that if individual firm charges price above the market price, it will not sell anything.
The curve is the same as marginal revenue curve because change in total revenue from selling one more unit(marginal revenue) is the constant market price.
And it holds in perfect market that price equals marginal revenue (P=MR).
The correct option is D.