An analyst does research about interest rate risk of fixed income securities and gathers the following information about three option-free bonds selling at par:
| Bond | Coupon Rate | Maturity (Years) |
| 1 | 5% | 4 |
| 9 | 5% | 9 |
| 3 | 7% | 9 |
The bond with the lowest interest rate risk is:（）
A. Bond 1.
B. Bond 2.
C. Bond 3.
