Which of the following statements about cost and revenue are correct? (A) In the short run, fixed costs remain constant, regardless of the level of output. (B) Marginal cost (MC) equals the change in total cost when an additional unit of output is produced. (C) Average total cost (ATC) is the total cost divided by the total output produced. (D) Revenue maximization occurs when marginal revenue (MR) exceeds marginal cost (MC).