In a banking system with limited reserves, which of the following best explains why a monetary policy might be ineffective in fixing an economy in some cases?

a. Commercial banks may keep excess reserves, reducing the total change in the money supply and the effectiveness of monetary policy.
b. Individuals in any economy are highly cautious, and they will hoard money even when the interest rate is changed due to the monetary policy.
c. Money supply in the economy is indifferent to interest rates, which is why monetary policy is sometimes an ineffective tool.
d. Open market operations have absolutely no impact on the credit creation process, which is why monetary policy is sometimes an ineffective tool.
e. Prices in the economy are very sticky in the long run, which is why any change in the money supply will have no change in the economy.