Which of the following statements regarding a sinking fund provision is TRUE A sinking fund provision:（）
A. requires that the issuer should set aside money based on a predefined schedule to accumulate the cash to retire the bonds at maturity.
B. requires that the issuer should retire a portion of the principal through a series of predefined principal payments over the life of the bond.
C. must be made through the payment of cash, paid to the trustee based on a predetermined schedule.