4. A fixed cost: A) doesn't change with the level of output in the short run. B) includes only sunk costs. C) grows as the level of output grows. D) refers only to costs for assets that don't move. 5. costs increase as the level of production increases. A) Implicit B) Fixed C) Variable D) Sunk 6. The additional cost of producing one more unit of a good is: A) average variable cost. B) total cost. C) variable cost D) marginal cost. 7. A firm's profit is maximized at the output level where: A) marginal cost equals marginal revenue. B) average fixed cost is minimized. C) variable cost is maximized. D) sunk cost is eliminated