The correct answer is: D. None of these
In the long-run, a monopolistic firm will produce at the point where marginal revenue equals marginal cost. However, the price that the firm charges will be greater than marginal revenue, and therefore greater than marginal cost. This is because a monopolistic firm is the only seller in its market, and it can therefore charge a price above the competitive price.
Option A is incorrect because it states that marginal revenue equals average revenue. This is only true in a perfectly competitive market, where there are many firms selling identical products. In a monopolistic market, marginal revenue is always less than average revenue.
Option B is incorrect because it states that price equals marginal revenue equals marginal cost. This is only true in a perfectly competitive market, where there are many firms selling identical products. In a monopolistic market, price is always greater than marginal revenue, and therefore greater than marginal cost.
Option C is incorrect because it states that marginal revenue equals marginal cost equals price equals average cost. This is only true in a perfectly competitive market, where there are many firms selling identical products. In a monopolistic market, marginal revenue is always less than average revenue, and therefore price is always greater than marginal revenue and marginal cost.