What could be the source of the problem?

Refer to the exhibit.

The network shown in the exhibits is configured with an active and standby controller that uses Layer 3 redundancy for AP termination. There are 100 APs provisioned into the AP Group NY1. The active local controller fails and the APs terminate on the standby local controller. Centralized licensing is enabled on the controller cluster with capacity for 100 APs. The WLAN clients are not able to SSID.

What could be the source of the problem?
A . The VLAN mapping is not configured on the standby local controller.
B . There are not enough licenses on the standby local controller to support the APs
C . The IP helper address on the interface VLAN is not configured on the standby local controller.
D . The uplink trunk of the standby controller does not permit the user VLANs for the SSID Layer 3 deployment.

Answer: A