There are two routers on the back-to-back interfaces of the routers, one of which is connected to the other via the following cables:MSR-Serial0/0]display interface Serial 0/0 Serial0/0 current state: UPLine protocol current state: UP Description: Serial6/0 InterfaceThe Maximum Transmit Unit is 1500, Hold timer is 10(sec) Internet Address is 6.6.6.1/30Link layer protocol is PPP LCP opened, IPCP openedFrom the above information, we can see that ﹣ we can see ﹣ that ﹣ can ﹣ know \\\\.
选项：

A: The router has completed the PPP negotiation with the remote device and successfully established the PPP link
B: PPP, PAP or chap verification options have been successfully completed between this router and the remote device. It is impossible to see whether there is a verification or not and whether it is passed
C: 6.6.6. It is not possible to Ping the end address of the router
D: The interface information indicates that the second IP address subordinate can also be configured under this interface