Economies of scale a. require inputs' MPP to fall as output increases (everything else equal). b. pertain to the long run only. c. refer to increased output generalized by an increase in the quantity of a single input. d. imply that the AC curve will fall continuously as output increases in the short run.

Economies of scale pertain to the long run only.

Explanation:

Economies of Scale is a long run phenomenon and is defined as the cost advantage that a firm experiences as a result of an increase in its output. The benefit arises as a result of the inverse relationship between quantity produced and per-unit fixed cost. The higher the quantity of output that are produced, the lower the per-unit fixed cost.

Economies of scale leads a fall in the average variable costs with an increase in the level of output. This is as a result of synergies and operational efficiencies which comes into place due to the increase in the scale of production. Economies of scale is a vital concept as it shows the competitive advantages big firms have over the small firms.