How does ERS use the VLAN tag?

How does ERS 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