The Main Reason Why the Economy's Aggregate Supply Curve Slopes

Multiple Choice

The main reason why the economy's aggregate supply curve slopes upward is that

A) as the price level rises, businesses incur additional costs.
B) businesses typically purchase labor and other inputs under long-term contracts that fix the cost of the input in money terms.
C) as the price level rises, workers have higher real wages to spend for additional consumer goods.
D) All of the above are correct.