The Term Diminishing Marginal Product Refers to A

The term diminishing marginal product refers to a:

A) falling real rate of interest that can be expressed relative to the marginal product of labor.
B) reduction in profits from producing to the point where marginal revenue is less than marginal cost.
C) decrease in total output due to the firm hiring unskilled workers.
D) decline in the marginal product of an input as you use more of that input.