The correct answer is A. MR=MC.
A monopolist is the only seller of a good or service in a market. This means that they have a great deal of market power and can set their own prices. However, they also face a downward-sloping demand curve, which means that they can only sell more goods or services by lowering their prices.
The marginal revenue (MR) curve for a monopolist is below the demand curve. This is because when a monopolist sells one more unit of output, they must lower the price of all units sold. This means that the marginal revenue from selling one more unit is less than the price of that unit.
The marginal cost (MC) curve for a monopolist is also below the demand curve. This is because the monopolist must incur additional costs to produce additional units of output.
The equilibrium for a monopolist occurs where the MR curve intersects the MC curve. At this point, the monopolist is maximizing their profits.
Option B is incorrect because the MC curve must intersect the MR curve below the demand curve.
Option C is incorrect because the price is not equal to the MR or MC curves.
Option D is incorrect because the AC curve is not relevant to the determination of equilibrium for a monopolist.