参考答案：B

解析：

CMOs are structured so as to redistribute prepayment risk and interest rate risk among the different classes, or tranches, of bonds using rules for the distribution of interest and principal. For example, if there are three classes of bonds, the distribution rules ensure that the first class of bonds receives all principal until they are completely paid off. Then the next class of bonds receives all principal until they are paid off. Finally, the last class receives principal payments. Effectively, the first tranche has the shortest maturity (duration) while the last tranche has the longest maturity (duration). Thus prepayment risk and interest rate risk have been redistributed across the bond classes with the first tranche experiencing the greatest prepayment risk and the last tranche experiencing the most interest rate risk.