Which statement describes a feature of this spanning-tree topology?

Refer to the exhibit. Which statement describes a feature of this spanning-tree topology?

A.
VLANs are restricted to access-switch pairs.

B.
Port density at the aggregation layer can be difficult.

C.
The use of distributed EtherChannel is recommended.

D.
Only one aggregation-to-access uplink is active at a given time.