What are possible reasons for this problem?

R1 is unable to establish an OSPF neighbor relationship with R3.

What are possible reasons for this problem? (Choose two)
A . All of the routers need to be configured for backbone Area 1.
B . R1 and R2 are the DR and BDR, so OSPF will not establish neighbor adjacency with R3.
C . A static route has been configured from R1 to R3 and prevents the neighbor adjacency from being established.
D . The hello and dead interval timers are not set to the same values on R1 and R3.
E . EIGRP is also configured on these routers with a lower administrative distance.
F . R1 and R3 are configured in different areas.

Answer: DF

Explanation:

To become OSPF neighbors, routers must meet these requirements: Hello interval, Dead interval and AREA number -> D and F are correct.