which two requirements to function correctly?

An IP-IP tunnel must meet which two requirements to function correctly? (Choose two.)

A.
The tunnel end points must have a valid route to each other.

B.
The tunnel end points must be distributed inside the IGP.

C.
A GRE tunnel must be established first to carry the IP-IP tunnel.

D.
All devices in between the tunnel end points must have a valid route to the tunnel end points.