The correct answer is D.

Because the short-run average total cost curve slopes downward for an information product, the firm experiences (D) a downward sloping marginal cost curve.

The marginal cost curve is a graphical representation of the short-run marginal costs of products or services and the total output. The marginal cost is the extra cost incurred for producing an additional item. A decline in the total cost (which makes the total cost curve decline) indicates a reduction in the total output, hence decreasing the product's marginal cost. This decline causes a drop in the marginal cost curve. The lower the output within a given period, the lower the marginal cost, while the higher the output, the higher the marginal cost incurred during that period. The total cost curve determines the direction of the marginal cost curve.

Cost:

The cost can be defined as the amount of money attached to something, either a product or service. In business, there are costs attached to labor, raw materials, and equipment purchasing. These costs depend on the type of work or production in question and the type of product being produced.