单选题 Which of the following most accurately describes the competitive structure that is characterized by a firm that operates with the lowest average total cost and has the capacity to produce all of an industry's output?

A. Oligopoly.
B. Competitive monopoly.
C. Natural monopoly.

【正确答案】 C

【答案解析】A natural monopoly is characterized by a single firm within the industry that has sufficient capacity to meet the entire demand of an industry because at that scale the lowest average total cost is achieved.