Answer: c. increase the discount rate.
Step-by-step explanation:
The discount rate of a country is the rate at which the central bank in that country loans money out to the financial institutions.
When this rate is low, more financial institutions will borrow money as opposed to when it is high. Banks borrowing money increases the money supply in the economy so if the Federal Reserve wants to reduce money supply, it should increase the discount rate which would dissuade banks from borrowing from the Fed thereby limiting money supply.