Select the appropriate definition for each of the following costs. A. Vary directly and proportionally with changes in volume B. Varies inversely with the activity leve. C. Remains constant in the short run, regardless of changes in activity. D. Constant over small ranges of output, but increases as levels of activity increase. Fixed cost per unit 2.Fixed costs in total 3. Variable cost per unit 4 Variable costs in total 5. Step costs