问题如下：
In the context of mortgage-backed securities, a conditional prepayment rate (CPR) of 8% means thatapproximately 8% of the outstanding mortgage pool balance at the beginning of the year is expected to be prepaid:
选项：
A.in the current month.
B.by the end of the year.
C.over the life of the mortgages.
解释：
B is correct.
CPR is an annualized rate, which indicates the percentage of the outstanding mortgage pool balance at the beginning of the year that is expected to be prepaid by the end of the year.
老师，我想就这道题问一下（1-smm）^12=1-CPR这个公式。为什么是“1-”？为什么不能直接SMM^12=CPR，这个含义没弄明白，视频讲解也是很理所当然的样子。。。
