In long-run, how ATC changes as the scale of production changes? a. When Q is low, Economies of scale happens because of specialization. As a result, ATC falls. b. When Q is medium, constant Economies of scale happens because the workers are at their best productivity level. As a result, ATC remains the same. c. When Q is large, because of the coordination problems, Diseconomies of scale happens . As a result, ATC rises. d. All of the above are correct.