An analyst does research about long-run equilibrium in monopoly markets. With respect to the regulation of a natural monopoly, a govemment subsidies sufficient to compensate the natural monopoly firm implies setting:

A. price equal to average cost.
B. price equal to marginal cost.
C. output where marginal cost equals marginal revenue.

在环境流行病学研究时采用设计按因素分层，分析阶段采用多元统计方法处理来解决

A．多因素
B．弱效应
C．非特异性
D．潜隐期
E．环境流行病学各特点