The correct answer is B. Marginal cost.
Marginal cost is the cost of producing one additional unit of a good or service. It is the change in total cost that results from producing one more unit of output. Marginal cost is usually increasing as output increases, because it takes more resources to produce each additional unit of output.
Average cost is the total cost divided by the number of units produced. It is a measure of the average cost of producing each unit of output. Average cost is usually decreasing as output increases, because the fixed costs are spread out over more units of output.
Fixed cost is the cost that does not change with the level of output. It includes costs such as rent, insurance, and depreciation. Fixed costs are always incurred, regardless of how much output is produced.
Variable cost is the cost that changes with the level of output. It includes costs such as labor, materials, and energy. Variable costs are incurred only when output is produced.
In conclusion, marginal cost is the cost of producing one additional unit of a good or service. It is the change in total cost that results from producing one more unit of output. Marginal cost is usually increasing as output increases, because it takes more resources to produce each additional unit of output.