A monopoly, unlike a perfectly competitive firm, assumes some market power. It can raise its price, within limits, without the quantity demanded falling to zero. The main way it retains its market power is through barriers to Entry-that Is, other companies cannot enter the market to create competition in that particular industry. Consider the market for tanzanite. The mines for this blue-purple gemstone, found only In Tanzania, are owned by the local government. Given that no one is allowed into the mines without government permission, the market structure for tanzanite highly resembles that of a monopoly. Which of the following best explain5 the barriers to entry that exist in this scenario?

a. Control of a scarce resource
b. Legal restrictions
c. Economies of scale