A pension fund's liabilities has a PV01 of $200 million. The plan has $100 billion of assets with a weighted average modified duration of 8. The highest duration bond that the plan can invest in has a modified duration of 28. How much of the existing assets should be invested in this bond with a modified duration of 28 to minimize the interest risk exposure of the fund?

A. $0

B. $20 billion

C. $40 billion

D. $60 Billion