问题
单项选择题
Firms in a perfectly competitive industry will increase their output until which of the following conditions is met（）
A. Total revenue equals price.
B. Marginal cost equals price.
C. Marginal revenue equals average fixed cost.
答案
参考答案：B
解析：
When a firm operates under conditions of perfect competition, marginal revenue always equals price. Under perfect competition, price is constant (a horizontal line) so marginal revenue is constant. Therefore a firm will increase output until marginal cost equals price.