What needs to be included in the design to avoid having the secondary controller go into maintenance mode?

Refer to the exhibit.

An enterprise is using wireless as the main network connectivity for clients. To ensure service continuity. a pair of controllers will be installed in a datacentre. An engineer is designing SSO on the pair of controllers .

What needs to be included in the design to avoid having the secondary controller go into maintenance mode?
A . The Keep alive timer is too low. which causes synchronization problems.
B . The connection between the redundancy ports is missing.
C . The redundancy port must be the same subnet as the redundancy mgmt.
D . The Global Configuration of SSO is set to Disabled on the controller.

Answer: D