Suppose that a society begins at a point inside its production possibilities frontier (PPF) and then ends up at a point on that same PPF. Which of the following could have caused such a change? a. The society started out using all of its resources, but then allowed some of its resources to become unemployed. b. The society developed an improvement in technology. c. The society had some unemployed resources to begin with, but then started using all of its resources. d. The society experienced an increase in the quantity of resources available