While your MPLS core is using Cisco routers, the core of a company you have acquired is not.
After extending your MPLS VPN networks by integrating the cores, you discover that the end-toend LPS path between PE routers cannot be established.
Which of the following may have caused this problem?

A.
the MTUs do not match

B.
the BGP protocol versions do not match

C.
MPLS is not supported between different vendors

D.
MP-BGP is not supported between different vendors

E.
you are using Cisco proprietary TDP in your existing core