问题如下：
In a perfect competitive market, a firm’s marginal revenue is always:
选项：
A.equal to the price per unit.
B.equal to the additional cost for one more unit.
C.equal to the average cost per unit.
解释：
In a perfect competitive market, the firm is price taker, therefore, marginal revenue is always the same as price per unit. In equilibrium, each firm will reach the position where P=MR=MC=ATC.
考点：完全竞争市场
解析：在完全竞争的市场中，企业是价格接受者，因此边际收益始终等于单位价格。在均衡状态下，各企业才会达到P=MR=MC=ATC的均衡。
老师 其实B的表达在就是A啊 只是A是完全竞争市场的特例？
