Which one of these statements is true concerning the data center distribution (aggregation) layer design?

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Which one of these statements is true concerning the data center distribution (aggregation) layer design?

A. With Layer 3 at the aggregation layer, the physical loops in the topology must still be managed by STP.
B. The boundary between Layer 2 and Layer 3 must reside in the multilayer switches, independent of any other devices such as firewalls or content switching devices.
C. A mix of both Layer 2 and Layer 3 access is sometimes the most optimal.
D. In a small data center, the aggregation layer can connect directly to the campus core, exchanging IP routes and MAC address tables.