A movement along the demand curve shows a change in demand

Which of the following does a social planner necessarily need to know to restore efficiency in a monopoly market?

A) The monopolist's marginal costs only B) The buyers' demand for a close substitute of the product sold in the market C) The monopolist's marginal revenue and the tax levied on the sale of the good D) The monopolist's marginal costs and the buyers' willingness to pay for the good

Which of the following is the reason why pharmaceutical firms are not monopolistically competitive?

A. Pharmaceutical firms sell differentiated products. B. There are many buyers in the market. C. There are many sellers in the market. D. There are barriers to entry in the market, like patents.