单选题 Which of the following most accurately describes the relationship between price (P), marginal cost (MC), and marginal revenue (MR) at the profit maximizing output level for a firm in a perfectly competitive industry?

A. P＞MC=MR.
B. P=MC=MR.
C. P＞MC＜MR.

【正确答案】 B

【答案解析】For a perfectly competitive firm, maximum profit occurs at the output level where marginal revenue equals marginal cost. And, since the demand curve faced by each firm in perfect competition is horizontal, marginal revenue is equal to price.