Under perfect competition in the long run,price is equal to

A) marginal revenue.
B) marginal cost.
C) average total cost.
D) All of the choices are equal to price under perfect competition.

Under perfect competition in the long run, the industry supply curve intersects the demand curve at the point where price is equal to the minimum point of the average total cost curve. This implies that price is equal to both marginal revenue and marginal cost at this point. So, options A and B are correct. Additionally, since price is also equal to the minimum point of the average total cost curve, option C is also correct. Hence, all of the choices are equal to price under perfect competition. Therefore, the correct answer is D.