Firms in monopolistically competitive industries cannot earn economic profits in the long run because

a. government regulators, whose first interest is the public good, will impose regulations that limit economic profits.

b. the additional costs of product differentiation will eliminate long-run economic profits.

c. economic profits will attract competitors whose presence will eliminate profits in the long run.

d. whenever one firm in the industry begins making economic profits, others will lower their prices, thus, eliminating long-run economic profits.