Which of the Following Explains Why We Assume That the Economy's

Multiple Choice

Which of the following explains why we assume that the economy's aggregate supply (AS) curve has a positive slope?

A) Inputs become more expensive at higher levels of output.
B) Inputs become less expensive at higher levels of output.
C) Firms' unit costs rise as output increases.
D) Firms' unit costs fall as output increases.
E) Aggregate demand increases at higher levels of national income.