When the economy is operating at potential GDP, an unannounced decrease in the rate of growth of the money supply intended to reduce inflation will most likely lead to. lower inflation and:（）
A. a decrease in output in both the short run and the long run.
B. no change in output in both the short run and the long run.
C. a decrease in output in the short run, and lower inflation but no change in output in the long run.