Which of the following describes the regulatory practice of setting prices at a level where the monopoly firm's average total cost curve intersects the demand curve（）

A. Average cost pricing.

B. Marginal cost pricing.

C. Cost-of-service pricing.

根据智齿与下颌外支及第二磨牙的关系，阻生齿完全位于外支内时称为

A．高位阻生
B．中位阻生
C．低位阻生
D．第Ⅱ类阻生
E．第Ⅲ类阻生