Answer:
The correct answer is the option B: marginal cost.
Step-by-step explanation:
To begin with, a monopoly is a situation of privilige where there is only one producer in the industry and this one offers its product at the quantity or the price he decides. Moreover, a monopolist will produce its product in a quantity level that matches with the point in the graphic where the marginal revenue equals the marginal cost of the production. This point is commonly known, in the microeconomic field, with the name of ''Pareto Efficiency''.