The process of entry and exit into a monopolistically competitive market continues until: (A) profits are positive. (B) profits are negative. (C) profits are zero. (D) Any of these statements could be true. 13. When economic profits are zero for a firm, it means that: (A) no firms will enter or exit the industry. (B) average revenue slightly above average total cost. (C) average variable costs are minimized. (D) accounting profits are also zero.