Routers R1 and R2, OSPF neighbors in area 0 over their Fa0／0 interfaces (respectively), cu

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