By how much did real investment decline between 1929 and 1933?

In the long run in perfect competition, firms will operate at

a. minimum average total cost. b. an average total cost that is just slightly above the minimum. c. an average total cost that is about 10% above the minimum. d. an average total cost that is below price.

When positive externalities are present, it means that:

A. society bears part of the cost borne of private transactions. B. individuals consume more than the social optimum. C. individuals don't take into account all the benefits associated with their market choice. D. All of these statements are true.