A mutual fund is holding a portfolio consists of four bonds. Duration of Bond A is 1.22-year, of Bond B is 2.75-year, of Bond C is 3.11-year, of Bond D is 5.16. The proportion of Bond A in the portfolio is 30%, Bond B is 25%, Bond C is 15%, and the rest goes to Bond D.

Which bond in the portfolio is exposed to the lowest interest rate risk? Briefly explain.