20. Company ABC is required to pay their customers $20,000 after 3 years. Andy, the company's actuary, is required to use some of the following bonds to construct a portfolio of assets that will fully immunize the potential interest rate risk. 1-year zero-coupon bond 2-year zero-coupon bond 3-year zero-coupon bond 4-year zero-coupon bond Assuming the market interest rate is 10%, determine the combination of zero-coupon bonds that has the lowest sum of par amount