Using Q-in-Q Virtual Local Area Network (VLAN) stacking, how does a carrier differentiate one customers traffic from tha

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Using Q-in-Q Virtual Local Area Network (VLAN) stacking, how does a carrier differentiate one customers traffic from that of another?

A. The provider edge (PE) switch adds an additional field called a PE tag to the customers Layer 2 data.
B. The PE switch replaces the customers VLAN tag with a carrier-assigned tag.
C. The PE switch adds a second VLAN tag to identify the customers traffic on the carriers network.
D. The PE switch assigns a customer-specific priority label to the customers traffic.