Which of the following statements is true

A) Total variable cost change in direct proportion to changes in the amount of the activity.
B) In the short run, all cost are variable.
C) In the long run, all costs are fixed.
D) Mixed costs are step costs.

Total Variable Cost

The sum of all variable costs associated with the production of goods or services, which increases or decreases based on production volume.

Cost Change

Any variation, either an increase or decrease, in the total costs associated with production or operations.

Mixed Costs

Expenses that contain both fixed and variable components, changing in total with the level of activity.