【单选题】
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
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