问题如下：
An investor is most likely to face the redemption risk when:
选项：
A. the bond is issued with a term maturity structure.
B. the bond is issued with a sinking fund.
C. the bond is a serial bond.
解释：
B is correct.
With a sinking fund arrangement, the issuer must redeem part of the issue before the maturity date.
sinking fund provision 的advantage 就是可以reduce credit risk, 因为periodic principal redemptions. 所以为什么还选B呢？ 以及A C各错在什么地方？