Answer:
Option (a) is correct.
Step-by-step explanation:
The Marginal product of labor is defined as the extra units of output produced from hiring one more labor. The formula for marginal product of labor is as follows:
Change in output per unit change in labor:

Graphically, the marginal product of labor is the slope of the production function for a particular firm and it is calculated by differentiating production function with respect to labor.