monopoly arises when a firm produces a good or service for which substitutes exist, and A. no close; produces an output at which diseconomies of scale exist B. no close; is protected by a barrier that prevents other firms from selling that good or service C. close; can influence the market price D. close; is protected by a barrier that prevents other firms from selling that good or service monopoly arises when a firm produces a good or service for which substitutes exist, and A. no close; produces an output at which diseconomies of scale exist B. no close; is protected by a barrier that prevents other firms from selling that good or service C. close; can influence the market price D. close; is protected by a barrier that prevents other firms from selling that good or service