In early 2009, the White House urged Congress to pass a package of temporary spending increases and tax cuts. It was a time when unemployment was soaring and many jobs were lost. Which sentence best illustrates one of the three principles of economy-wide interactions?

a. The Government was working to provide equity in the markets.
b. That Government policies can change spending by increasing people's after-tax incomes.
c. There are marginal costs that the Government can adjust.
d. More money would be available to trade.