How do you test end-to-end data flow between PE-routers?

How do you test end-to-end data flow between PE-routers?

A.
Use the ping vrf command from the local PE-router to ping the remote PE router’s loopback address.

B.
Use the telnet command from the local PE-router to access the remoter PE-router’s loopback address.

C.
Use the traceroute command from the local PE-router to the remoter PE-router’s loopback address.

D.
Because PE-PE traffic is done via label switching over an LSP, end-to-end data flow cannot be tested. You must test from CE to CE-router.

Explanation:

Not A: You cannot issue "ping vrf" to a loopback, when other end’s loopback is not part of VPN.