On a diagram of a production possibilities frontier, opportunity cost is represented by the slope of the production possibilities frontier

If electric utilities continually reduce their emissions of sulfur dioxide

A) the utilities will eventually be forced to go out of business. B) the marginal cost of further emissions will rise. C) the marginal benefit of additional emissions will rise. D) the total benefit of sulfur dioxide emissions will fall.

Over the past five decades, the U.S. civilian unemployment rate has varied between, roughly, ________

A) 3% and 11% B) 55% and 60% C) 6% and 8% D) 0.2% to 0.4%