Answer:
a. influences aggregate supply but fiscal policy influences aggregate demand.
Step-by-step explanation:
Remember, when the term monetary policy is used it refers to policies that are focused on the interest rates as well as the inflation rate, which certainly affects the money supply specifically. However, the fiscal policy is usually channelled towards aggregate demand of the economy.
Thus, it is right to say that one important difference between monetary and fiscal policy is that monetary policy affects aggregate supply but fiscal policy influences aggregate demand.