单选题 If the economy is in short-run disequilibrium below full employment, the most likely explanation is that:

A. aggregate demand has decreased.
B. long-run aggregate supply has decreased.
C. resource prices have decreased.

【正确答案】 A

【答案解析】A decrease in aggregate demand can reduce output below its full-employment level. A decline in long-run aggregate supply would mean the full-employment output level itself has decreased. Resource prices and wage rates are assumed to be fixed in the short run, but the long-run effect of decreases in wage rates and resource prices would be to increase (shift) short-run aggregate supply, leading to an increase in output.