为什么c是错的？

问题如下：

Three firms operate under perfect competition, producing 900 units of the same product but using different production technologies. Each company's cost structure is indicated in the table:

Which of the following statements is most accurate? If the unit selling price is:

选项：

A.$4.50, all firms should continue to operate in the short run, but exit the market in the long run if these conditions are expected to persist. B.$3.00, Firm X should continue to operate in the short run, but Firms Y and Z should shut down production. C.$6.00, all firms should exit the market in the long run.

解释：

Solution: B

中文解析：

由英文解析表格可知，如果售价是3美元，所有公司的总收入将是3.00美元/单位× 900单位= 2700美元。只有企业X的可变成本被覆盖，它应该继续运营，而企业Y和Z应该立即停产。