听力原文：M: Banks may borrow emergency funds from the Fed to meet an unusual demand for ca
W: Thus, Fed serves as a source of last resort for emergency funds. It is one of the major objectives of the Federal Reserve System.
Q: What will the banks do when there is an unusual demand for cash by depositors？
A．To serve as a source of last resort.
B．To be one of the major objectives.
C．To transfer depositors' funds from one bank to another.
D．To borrow emergency funds from the Fed.