NO.PZ2018062012000005
问题如下：
From the lender's perspective, when the interest rates rises, which risk of the mortgage securities is most likely to confront with:
选项：
A. yield maintenance.
B. extension risk.
C. contraction risk.
解释：
B is correct.
When interest rates rise, homeowners are unwilling to give up the benefits of the contractual interest rate that now looks low, so the prepayments will be lower than expected. The security backed by mortgages will have longer maturity than was anticipated at the time of purchase. The risk under such circumstances is extension risk. The contraction risk is when the interest rate decline, actual prepayments will be higher than expected, the security backed by mortgages will have shorter maturity than was anticipated at the time of purchase.
这道题为什么选b呢？