牙源性腺样瘤是混合性牙源性肿瘤的病理依据是()

A．肿瘤含有玫瑰花样结构

B．肿瘤含有腺样结构

C．肿瘤含有小结节

D．肿瘤含有釉基质和牙本质基质

E．肿瘤含有淀粉样物质

A profit maximizing firm will expand output as long as marginal revenue is:（）

A. less than marginal cost.

B. greater than marginal cost.

C. less than average variable cost.