参考答案：C

解析：

A feedback-rule monetary policy that focuses on GDP growth will increase the growth rate of the money supply in response to the decrease in real GDP from a productivity shock (a decrease in potential GDP growth due to a reduction in productivity growth). The resulting increase in aggregate demand will increase the price level compared to a fixed-rule policy (of money supply growth) and compared to a feedback-rule policy focused on the price level, which would indicate a reduction in money supply growth based on the price level increase following a productivity shock. A fixed-rule policy does not focus on changes in either the price level or the rate of GDP growth.