Immunization in Liability-Driven Strategies

In the context of liability-driven investment strategies, immunization is a key approach that seeks to manage interest rate risk to ensure that a portfolio's present value of assets matches the present value of its liabilities. Consider the following scenario:

A pension plan is considering two different investment strategies for its bond portfolio. The plan has a duration of liabilities of 7 years, and it wishes to manage the interest rate risk associated with those liabilities effectively. The investment committee is evaluating the following bond portfolios:

1. **Portfolio A**: Consists of bonds with a duration of 5 years.

2. **Portfolio B**: Consists of bonds with a duration of 8 years.

Given these options, which portfolio would better achieve the goal of immunization for the pension plan?