利率上升，不提前还款，就是按计划还款，按计划还款怎么可能有extension risk 呢？只有到了计划还款时间点还不上了，要求延期，才会产生extension 啊？

问题如下：

If interest rates increase, an investor who owns a mortgage pass-through security is most likely affected by:

选项：

credit risk.

extension risk.

contraction risk.

解释：

B is correct.

Extension risk is the risk that when interest rate rise, fewer prepayments will occur. Homeowners will be reluctant to give up the benefit of a contractual interest rate that is lower. As a result, the mortgage passthrough security becomes longer in maturity than anticipated at the time of purchase.

考点：延期风险

解析：当利率上升时，homeowner不会选择提前还款，这样一来导致的风险就是extension risk，即延期风险，故选项B正确。