Which of the following is the least tangible?

When price is $10 the monopolist can sell 100 units. In order to sell 101 units, the price must fall to $9 . Which of the following is the monopolist's marginal revenue from selling the 101st unit?

a. -$91. b. $10 c. $99 d. $909

It is the custom for paper mills located alongside the Layzee River to discharge waste products into the river. Operators of hydroelectric generating plants on the river find they must clean up the river's water before it flows through their equipment. The above situation is an example of:

A. an external economy. B. the exclusion principle. C. a spillover cost. D. a spillover benefit.