Which of the Following Is the Difference Between Variable Costs

Which of the following is the difference between variable costs and fixed costs?

A) Variable costs are the costs incurred on variable factors of production, whereas fixed costs are the costs incurred on all factors of production.
B) Variable costs of a firm are zero after a firm shuts down, whereas the firm continues to incur the fixed costs of production in the short run.
C) Variable costs exist even when production is zero, whereas fixed costs exist only when there is some positive level of production.
D) Variable costs are incurred by a firm only in the long run, whereas the firm incurs some fixed costs in both the short run and the long run.