Which of the following statements is correct? A) In a monopolistically competitive equilibrium price is chosen such that P=AC. B) In a duopoly, there is negative relationship between a typical Cournot firm's marginal revenue and the elasticity of the residual demand curve such a firm faces. C) In a monopoly, strategic entry barriers are always the result of absolute cost advantages. D) Under perfect competition, in the short run there is insufficient time for new firms to enter the industry which leads to the result that firms always make positive supernormal profits