NO.PZ2018062003000052
问题如下：
Which of the following descriptions about perfectly competitive market is most likely correct?
选项：
A.
In the long run, a firm can only earn normal profits.
B.
In the long run, there are opportunities for a firm to gain positive economic profits.
C.
In the long run, a firm will have negative economic profits
解释：
A is correct.
Under the perfect competition, price is equal to marginal cost in the long run, therefore a firm can only gain normal profits.
考点：正常利润。
解析：在完全竞争的市场条件下，厂商的利润为正常利润，即经济利润为0。
因为如果经济利润大于0，那么会有更多的厂商进入该市场瓜分利润，从而让经济利润降低为0.
如果经济利润小于0，那么现在市场中的厂商会退出市场，供给减少，价格增加从而使得留下的那些厂商的经济利润由负数上升到0.
何老师说如果有厂商退出长期完全竞争市场，那价格会短暂地上调，难道不能说这个时候有办法有赚超过normal profit吗、
