问题如下：
If a mortgage borrower makes prepayments without penalty to take advantage of falling interest rates, the lender will most likely experience:
选项：
A.extension risk.
B.contraction risk.
C.yield maintenance.
解释：
B is correct.
Contraction risk is the risk that when interest rates decline, actual prepayments will be higher than forecasted. Extension risk is the risk that when interest rates rise, prepayments will be lower than forecasted. Yield maintenance results from prepayment penalties; the lender is protected from loss in yield by the imposition of prepayment penalties
请问C什么意思？在哪章哪节出现的？
