Choice "D" is correct. Since price is barely sufficient to give a firm a normal profit and stay in business, the consumer obtains the product at as low a price as is economically feasible. In addition, every firm is forced to produce at the most efficient output rate.
Choice "b" is incorrect. Brand differentiation is present in monopolistic competition, not perfect competition.
Choice "c" is incorrect. This is not an appropriate application of the "consumer surplus" concept.
Choice "a" is incorrect. Individual consumers are also price takers at the market equilibrium price.
