问题：

[单选] 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.