Consider a firms per-period (e.g., hourly) production process. If it employs 1 unit of labor, then 5 units of output will be produced; if it employs 2 units of labor, then 12 units of output will be produced; and if it employs 3 units of labor, then 20 units of output will be produced. It follows that:
a. total output is increasing at an increasing rate and the marginal product of labor is increasing
b. total output is increasing at an increasing rate and the marginal product of labor is decreasing
c. total output is increasing at an increasing rate and the marginal product of labor is constant
d. total output is increasing at a decreasing rate and the marginal product of labor is decreasing
e. total output is increasing at a decreasing rate and the marginal product of labor is increasing
f. total output is increasing at a decreasing rate and the marginal product of labor is constant