视功能的客观检查是
A．体视觉B．视觉电生理C．视力D．视野E．色觉
参考答案：B
股票交易只可以在证券交易所进行。（）
Which of the following regarding monopolistic competition is TRUE（）
A. Zero barriers to entry and exit exist.
B. The demand curve for an individual firm is a straight horizontal line.
C. Each firm produces a differentiated product.
