Which of the following definitions describe marginal cost ?

(A) The variable cost of one unit of product or service
(B) A principle whereby variable costs are charged to cost units and the fixed costs attributable to the relevant period are written-off in full against the contribution for that period
(C) Costs appropriate to aiding the making of specific management decisions
(D) The price at which material identical to that which is used up could be replaced on the date of usage