Refer to the figure below. In response to gradually falling inflation, this economy will eventually move from its short-run equilibrium to its long-run equilibrium. Graphically, this would be seen as 

Which one of the following is not a possible barrier to entry high enough to keep competing firms out of a monopoly industry?

A) large economies of scale that result in a natural monopoly B) The monopoly firm has control of a key resource necessary to produce a good. C) a high concentration ratio D) There are important network externalities in supplying a good or service.

In a perfectly competitive market buyers want to buy 20,000 units and sellers want to sell 20,000 units of a product when the price is $50 per unit. ABC Corporation, one seller in this market, 

A. will sell a fixed number of units regardless of how the price changes. B. faces a downward-sloping demand curve for its product. C. will maximize profit by selling at a price less than $50. D. faces a perfectly elastic demand curve at a price of $50.