Concept:Marginal cost measures the change in total cost when one extra unit is produced.
Explanation:When output increases by one unit, the cost that rises is called marginal cost.
It is calculated as
MC=ΔQΔTC, where
ΔTC is the change in total cost and
ΔQ is the change in output.
Fixed cost does not change with output, so it is not the extra cost per unit.
Total cost is the sum of all costs, and average cost is the cost per unit, not the extra cost of one more unit.
Therefore, the additional cost incurred by producing an additional unit is marginal cost.
Answer:D. Marginal cost