Which of the Following Correctly Defines the Marginal Product of Labor

Which of the following correctly defines the marginal product of labor?

A) It is the additional output produced by an additional unit of labor, all other factors held constant.
B) It is the additional output produced by a proportionate increase in capital and labor, the demand for the product held constant.
C) It is the additional labor required to produce one additional unit of output, other inputs held constant.
D) It is calculated as the total output divided by the total units of labor employed in production.
E) It is the addition to total cost from employing an additional unit of labor.