In the late 1990s, the United States experienced very high GDP growth, record low unemployment rates, and virtually nonexistent inflation. Based on the conclusions of the AD/AS model, this combination of good economic results can be explained by a __________.
a. rightward shift of the aggregate demand.
b. leftward shift of the aggregate demand.
c. rightward shift of the short- or long-run aggregate supply.
d. leftward shift of the short- or long-run aggregate supply.