The Federal Reserve System performs many functions, but its most important one is

a. issuing currency.

b. controlling the money supply.

c. providing for check clearing and collection.

d. acting as a fiscal agent for the U. S. government.

b. controlling the money supply.

Explanation:

The main function of the federal reserve is to control the money supply. This is accomplished through expansionary or contractionary monetary policies, in which the Federal Reserve influences the amount of economy in the economy by controlling its supply. An open marketing policy, ie selling and buying securities, for example, is used to control the amount of currency in the economy.