【单选题】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.
. marginal product; increasing; average fixed cost; decreasing
B.
. average variable cost; decreasing; average fixed cost; increasing
C.
. average total cost; increasing; marginal cost; decreasing
D.
. marginal product; increasing; average variable cost; decreasing