Which of the Following Explains Why the Aggregate Supply Curve

Multiple Choice

Which of the following explains why the aggregate supply curve is generally upward sloping?

A) When real output decreases, per-unit production costs tend to increase.
B) When aggregate demand shifts rightward, aggregate supply also always shifts rightward as well.
C) When real output increases, per-unit production costs decrease.
D) When real output increases, per-unit production costs increase as well.