摄影构图应做到（）。

A.必须有一个主题能够表达作者创作意图的“中心思想”

B.把观众的趣味中心集中到被摄中心——被摄主体上

C.必须画面简洁，只拍摄与主体密切相关的内容，排除或压缩分散注意力的内容

D.控制景深和虚实

With respect to regulating a natural monopoly, which of the following pricing rules to regulate the natural monopoly firm will most likely require the government to provide a subsidy sufficient to compensate the firm in order to avoid the firm to leave the market（）

A. Average cost pricing.

B. Marginal cost pricing.

C. Profit maximizing pricing.