All of the following statements, except one, are conect about a fim operating under conditions of either monopolistic competition or oligopoly. Which is the exception A) Graphically, it faces a downwardesloping demand curve. B) It charges a price above marginal cost in both the short run and the long run. C) It charges a price equal to average cost in both the short run and the long run. D) It fails to achieve economic efiiciency. E) It fails to achieve productive efirciency.