Which one of the following statements concerning marginal costing is NOT true?

A$.$

Contribution is calculated as sales revenue minus fixed cost of sales.

B$.$

Marginal cost is the cost of a unit which would not be incurred if that unit were not produced.

C$.$

Marginal costing is an alternative method of costing to absorption costing.

D$.$

Fixed costs are treated as a period cost and are charged in full to the income statement of the accounting period in which they are incurred.