Which of the following is a true statement? a. Decreasing returns to scale and diminishing marginal product are two ways of stating the same thing. b. Increasing returns to scale is a short-run concept, and diminishing returns to production is a long-run concept. c. SR costs exceed LR cost because they include fixed costs and LR cost do not include fixed costs. d. All the above are true. e. None of the above is true.