What will occur when the primary RADIUS fails then recovers?

An engineer has configured passive fallback mode for RADIUS with default timer settings.

What will occur when the primary RADIUS fails then recovers?
A . RADIUS requests will be sent to the secondary RADIUS server until the secondary fails to respond.
B . The controller will immediately revert back after it receives a RADIUS probe from the primary server.
C . After the inactive time expires the controller will send RADIUS to the primary.
D . Once RADIUS probe messages determine the primary controller is active the controller will revert back to the primary RADIU

Answer: C