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.
老师好，我想问的是prepayment for the month = SMM*( beginning outstanding mortgage balance for the month - scheduled principal repayment for the month) 这里不是用月末的贷款余额来乘以SMM吗，为什么题目选项说是以年初的余额的一定比例来算提前还款呢
