问题如下：
In a perfectly competitive market, the firm's short-term operating breakeven point is:
选项：
A. where average total cost is equal to its price level.
B. where marginal revenue curve intersects with its marginal cost curve.
C. where marginal revenue curve intersects with its average variable costs.
解释：
A is correct.
In a perfectly competitive market, price = marginal revenue = average total cost when the firm's operating is breakeven in the short term.
考点：盈亏平衡点
解析：盈亏平衡点下：边际收益=平均总成本。
在完全竞争的市场条件下，边际收益=商品价格
所以可得，价格=平均总成本，A选项正确。
B选项是利润最大化的条件
C选项是打酱油的选项。
这道题目b选项，其实不能算错吧，只是a更明确？
