How does the Ethernet Relay Service use the VLAN tag？（）

• A、 to provide service internetworking
• B、 to support transparency for Layer 2 frames
• C、 as a connection identifier to indicate destination
• D、 as a mapping to the DLCI in service internetworking
• E、 to provide a trunk by which all VLANs can navigate from one site to one or multiple sites