Router R1 has been configured with the commands rout er eigrp 9 and network 172.16.2.0 0.0.0.255, with no other current EIGRP configuration. R1's (working) Fa0/0 interface has been configured with IP address 172.16.2.2/26. R1 has found three EIGRP neighbors reachable via interface Fa0/0, including the rou ter with IP address 172.16.2.20. When the engineer attempts to add the neighbor 172.16.2.20 fa0/0 command in EIGRP configuration mode. Which of the following occurs？（）

• A、Fa0/0 fails
• B、The command is rejecteD
• C、The existing three neighbors fail
• D、The neighborship with 172.16.2.20 fails and then reestablishes
• E、None of the other answers is correct