问题
单项选择题
Which of the following most accurately describes a market structure that has one seller of a specific, well-defined product that has no good substitutes（）
A. Oligopoly.
B. Monopoly.
C. Monopolistic competition.
答案
参考答案：B
解析：
A monopoly is characterized by one seller, a specific and well-defined product for which there is no good substitutes, and high barriers to entry.