Routers R1 and R2, OSPF neighbors in area 0 over their Fa0/0 interfaces (respectively), currently both successfully use OSPF MD5 authentication. The OSPF configuration includes the area 0 authentication command under the router ospf 1 command. Which of the following commands must have been configur ed on R1's Fa0/0 interface?（）

• A、ip ospf authentication null
• B、ip ospf authentication message - digest
• C、ip ospf authentication -key whatever- it - is
• D、ip ospf message - digest - key 1 md5 whatever - it - is
• E、ip ospf md5 1 key whatever - it - is