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 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.