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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.$6.00, all firms should exit the market in the long run.

B.$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.

C.$3.00, Firm X should continue to operate in the short run, but Firms Y and Z should shut down production.

解释：

C is correct.

TR = Total Revenue; TC = Total Costs; TVC = Total Variable Costs; TFC = Total Fixed Costs

Hence, if the selling price is $3.00, total revenue for all firms will be $3.00/unit × 900 units = $2,700. Only Firm X’s variable costs are covered and it should continue operating, while Firms Y and Z should immediately shut down production.

A is incorrect. If total revenue equals or exceeds total costs, the firms should remain in the market both in the long and short run: each firm is just earning an economic profit, which includes its opportunity cost.

B is incorrect. At $4.50, total revenue is $4.50 × 900 = $4,050. Only Firms X and Y cover their variable costs; Firm Z should shut down. It is true, however, that if conditions persist, all should shut down in the long run as they won’t be covering their total costs.

中文解析：

依据英文解析截图，我们知道：

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的可变成本得到支付，它应该继续运营，而企业Y和企业Z应该立即停产。

A不正确。如果总收入等于或超过总成本，那么企业在长期和短期内都应该留在市场上:每个企业都只赚取经济利润，其中包括其机会成本。

B不正确。在4.50美元时，总收益为4.50美元× 900 = 4050美元。只有公司X和公司Y支付他们的可变成本;Z公司应该关闭。然而，如果情况持续下去，从长远来看，所有这些工厂都应该关闭，因为它们无法收回全部成本。