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

Explanation:
Ethernet Relay Service (ERS): A point-to-point VLAN-based E-line service that is used primarily for establishing a point-to-point connection between customer
routers
Cisco ERS is a point-to-point VLAN-based E-line service that supports service multiplexing, where multiple instances of service or EVCs can be multiplexed onto a
single customer UNI.
Service multiplexing means that many connections can be provided over one link. The multiplexed UNI supports point-to-point or point-to-multipoint connections
between two or more customer-specified sites, similar to a Frame Relay service. Instead of the data-link connection identifier (DLCI), the connection identifier in
ERS is a VLAN tag. Each customer VLAN tag is mapped to a specific Ethernet virtual connection.
ERS uses the VLAN to indicate destination. Therefore, the Ethernet service is not transparent to Layer 2 Ethernet frames—the VLAN tag dictates destination. The
ERS EVC does not act like a trunk where all VLANs go from one site to one or multiple sites.
ERS uses different point-to-point VLANs to connect one site to other remote sites.
If multipoint connections are available, the service is referred to as an Ethernet Relay Multipoint Service (ERMS): A multipoint-to-multipoint VLAN-based ELAN
service that is used primarily for establishing a multipoint-to-multipoint connection between customer routers.