If a firm holds a pure monopoly in the market and is able to sell 5 units of output at $4.00 per unit and 6 units of output at $3,90 per unit, it will produce and sell the sixth unit if its marginal cost is A. $3.90 or less B. $3.40 or less C. $3.50 or less D. $4.00 or less Answer: B