.Refer to the exhibit and the partial configuration on routers R1 and R2. Hot Standby Routing  Protocol （HSRP） is configured on the network to provide network redundancy for the IP traffic. The  network administrator noticed that R2 does not become active when the R1 serial0 interface goes  down.  What should be changed in the configuration to fix the problem？ （）

• A、 The Serial0 interface on router R2 should be configured with a decrement value of 20.
• B、 The Serial0 interface on router R1 should be configured with a decrement value of 20.
• C、 R2 should be configured with a standby priority of 100.
• D、 R2 should be configured with a HSRP virtual address.