What effect does the entry of new firms have on the economic profits of existing​ firms? When new firms enter a monopolistically competitive​ market, the economic profits of existing firms A. will because their demand curves will become more . B. will increase because their average cost of production will decrease. C. will remain unchanged because they sell differentiated products. D. will decrease because their demand curves will shift to the left. E. will decrease because their demand curves will shift to the right.