"Diminishing marginal​ returns" refer to a situation in which the ______.A. average product of the last worker hired is less than the average product of the previous worker hired.B. marginal cost of the last worker hired is less than the marginal cost of the previous worker hired.C. marginal product of the last worker hired is less than the marginal product of the previous worker hired.D. average cost of the last worker hired is less than the average cost of the previous worker hired.