参考答案：C

解析：

The marginal revenue product is the addition to total revenue from selling the additional output that one more unit of an input can produce. The additional output that results from employing one more unit of a productive input is the marginal product. The gain in total revenue from selling one more unit of output is the marginal revenue. A marginal revenue product exists for any level of output; it is not limited to the level at which marginal revenue equals marginal cost.