Concept:A firm maximizes profit by producing where marginal cost equals marginal revenue (MC=MR).Explanation:From the diagram, the profit-maximizing output is where the MC curve cuts the MR curve.At this point, the cost of producing one extra unit equals the revenue gained from selling it.In the given graph, MC=MR occurs at an output level of 900 units.Therefore, producing beyond this point would reduce profit, and producing less would mean forgoing extra profit.Answer:C. 900
