The required reserve ratio is:

a. the minimum amount of reserves the Fed requires a bank to hold.
b. the interest rate that the Fed charges banks who borrow from it.
c. the interest rate on loans made by banks to other banks.
d. the maximum percentage of the cost of a stock that can be borrowed from a bank, with the stock offered as collateral.
e. an appeal by the Fed to banks, asking for voluntary compliance with the Fed's wishes.

a