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;zero
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

When marginal cost is decreasing, it implies that each additional unit of output is costing less to produce than the previous one, which typically happens when the marginal product of labor (or other inputs) is increasing. This is because the firm is becoming more efficient in its production process. Additionally, if the marginal cost is decreasing, the average variable cost must also be decreasing because the cost of producing each additional unit is lower, thus pulling the average variable costs down.