In Regard to Banking and a Nation's Money Supply, the Discount

In regard to banking and a nation's money supply, the discount rate is the:

A) interest rate that banks must pay to borrow from the central bank.
B) reduction in interest rates that is given to a bank's preferred customers on their loans.
C) percentage reduction in inflation that is achieved through a monetary policy action.
D) interest rate that a bank pays to borrow another bank's excess reserves.