Which statement about data center access layer design modes is correct?（）

• A、The access layer is the first oversubscription point in a data center design.
• B、When using a Layer 2 loop-free design, VLANs are extended into the aggregation layer.
• C、When using a Layer 2 looped design, VLANs are not extended into the aggregation layer.
• D、When using a Layer 3 design,stateful services requiring Layer 2 connectivity are provisioned from the aggregation layer.
• E、The data center access layer provides the physical-level connections to the server resources and only operates at Layer 3.