Suppose the marginal cost curve in the short run first decreases and then increases. If marginal cost is decreasing, _____ must be _____ and _____ must be _____.
A. average total cost; increasing; marginal cost; decreasing
B. marginal product; increasing; average fixed cost; decreasing
C. average variable cost; decreasing; average fixed cost; increasing
D. marginal product; increasing; average variable cost; decreasing