砖砌体“三一”砌筑法的具体含义是指（）。

A.一个人

B.一铲灰

C.一块砖

D.一挤揉

E.一勾缝

Which of the following statements regarding a monopolist is most accurate （）

A. A monopolist will maximize the average profit per unit sold.

B. If a firm has a monopoly, it will always be able to earn economic profits.

C. A monopolist, like any other profit-maximizing firm, will sell at the output level where marginal revenue equals marginal cost.