Which of the following statements about control words in the L2VPN are true?

Which of the following statements about control words in the L2VPN are true?
A . When SVC VLL is used, if PEs at two ends of a VC use different control words, the may not become Up.
B . When Martini VLL is used, if PEs at two ends of a virtual connection (VC) use different control words, the VC may not become Up
C . The control word can be used to identically the packet sequence.
D . A control word generally has two bytes and can ne extended to four bytes.
E . The control word can be used for packet padding For example, when the public network uses
Ethernet and the AC uses Peer-to-protocol (PPP), control words can be used to transfer and identify
PPP packet with a bytes.

Answer: D