40. When an industry is in long-run equilibrium economic profits are _ and will be entering or leaving the industry. (LO5) a) zero, some b) zero, none c) positive, some d) positive, none 41. If a perfectly competitive firm sells 10 units of output at a price of $10 per unit, its marginal revenue per unit is (LO1) a) $1 b) $10 c) $100 d) more than $1, but less than $10 e) more than $10, but less than $100