The monopolistically competitive firm's economic profits tend toward zero in the long run. Why is this so? Select one: O a. Monopolistically competitive firms are rarely able to maintain the corporate discipline necessary to sustain profits in the long run. O b. Even though the monopolistically competitive firm can successfully maintain barriers to entry, keeping competition at bay becomes very expensive. O c in the long run, other firms will successfully offer substitutes for the profitable firm's product, and competition will eliminate economic profits. O d. If a monopolistically competitive firm is profitable for more than 2 years, the Justice Department orders a corporate restructuring to pull the company back to a normal rate of return