A router is able to assign labels to the prefixes and MPLS is enabled on all of the router interfaces.
However, this router is unable to establish an LDP session with its LDP neighbors. What could be
the cause of this problem?

A.
ip cef is not enabled.

B.
mpls ip is missing in the global configuration mode.

C.
The LDP router ID is unreachable.

D.
LIB has no label.