I need help with these questions

It is argued that monopoly pricing requires "barriers to entry". Otherwise, new firms would eventually erode the economic profits of the monopolist by entering the industry. Which of the following would n_otbe considered a barrier to entry? 0 inefficiency due to bureaucratic decision-making procedures 0 technological superiority O patents on a production process 0 exclusive ownership of essential raw materials 0 cost advantages in production resulting from natural monopoly Assume a single-price monopolist can sell 10 units of its product at a price of $45 each but to sell 11 units, the monopolist must cut price to $44. What is the marginal revenue of the extra unit sold