[单选题]Variable costs can be defined as the costs that: A. remain constant for all time periods. B. remain constant over the short run. C. vary directly with sales. D. are classified as noncash expenses. E. are inversely related to the number of units sold. Difficulty: 1 Easy Topic: Fixed and variable costs Learning Objective: 11-03 Determine and interpret cash, accounting, and financial break-even points.