The top four firms in the industry have 10 percent, 8 percent, 8 percent, and 6 percent of the market. The four-firm concentration ratio of this market is:

Economics

A) is a social science. B) is concerned with limited resources. C) is concerned with unlimited wants. D) All of the above are correct.

Which of the following could decrease the labor-supply curve for teachers?

a. a decrease in the wages paid to teachers b. an increase in immigration c. a change in the work preferences of men, with more of them preferring to be stay-at-home fathers d. any factor that would decrease the labor-demand curve