Answer: diminishing marginal product
Explanation:
A. When a firm in the market increase its level of production it results in reduction of cost which is called economies of scale.
B. Increase in cost that resulted due to unnecessary increase in level of production is called diseconomies of scale.
C. Increasing marginal product can be defined as the increase in output resulting due to employment of one more unit of input such as labor.
D. Diminishing marginal product can be defined as the decrease in output resulting due to employment of one more unit of input such as labor.
From the above explanation we can conclude that right answer is diminishing marginal product .