The correct answer is: A. Additional cost.
Marginal cost is the change in total cost that arises when one additional unit of a good or service is produced. It is the cost of producing one more unit of a good or service, given that all other inputs are held constant.
Full cost is the total cost of producing a good or service, including both fixed and variable costs. Fixed costs are costs that do not change with the level of output, such as rent or insurance. Variable costs are costs that change with the level of output, such as the cost of raw materials or labor.
Pure cost is a cost that is not associated with any specific output. It is a cost that must be incurred regardless of the level of output. For example, the cost of rent is a pure cost because it must be paid even if no output is produced.
In conclusion, marginal cost is the additional cost of producing one more unit of a good or service. It is the cost of producing one more unit of a good or service, given that all other inputs are held constant.