A pension fund has an average duration of its liabilities equal to 15 years. The fund is looking at 8-year maturity zero-coupon bonds and 5% yield perpetuities to immunize its interest rate risk. How much of its portfolio should it allocate to the zero-coupon bonds to immunize if there are no other assets funding the plan?

A. 55%

B. 37.5%

C. 46%

D. 40%