问题如下：
To illustrate SD&R’s immunization approach for controlling portfolio interest rate risk, Compton discusses a hypothetical portfolio composed of two non-callable, investment-grade bonds. The portfolio has a weighted average yield-to-maturity of 9.55%, a weighted average coupon rate of 10.25%, and a cash flow yield of 9.85%.
The two-bond hypothetical portfolio’s immunization goal is to lock in a rate of return equal to:
选项：
A.9.55%.
9.85%.
10.25%
解释：
B is correct.
Immunization is the process of structuring and managing a fixed-income portfolio to minimize the variance in the realized rate of return and to lock in the cash flow yield (internal rate of return) on the portfolio, which in this case is 9.85%.
请老师略微指点一下 two-bond hypothetical portfolio’s immunization 的内容
