人工呼吸有效的标志是（）.

A、瞳孔扩大

B、颈动脉博动

C、呼吸恢复

Which of the following is least accurate with regard to advertising for firms operating under monopolistic competition（）

A. The increase to average total costs associated with advertising increases as output increases.

B. Advertising expenses are high relative to perfect competition and monopoly.

C. Advertising is necessary to communicate the unique features of a firm’s products.