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 provisionedfrom the aggregation layer.
- E The data center access layer provides the physical-level connections to the server resourcesand only operates at Layer 3.