What is the best description of the HA4 Keep-Alive Threshold (ms)?

What is the best description of the HA4 Keep-Alive Threshold (ms)?
A . the maximum interval between hello packets that are sent to verify that the HA functionality on the other firewall is operational.
B . The time that a passive or active-secondary firewall will wait before taking over as the active or active-primary firewall
C . the timeframe within which the firewall must receive keepalives from a cluster member to know that the cluster member is functional.
D . The timeframe that the local firewall wait before going to Active state when another cluster member is preventing the cluster from fully synchronizing.

Answer: C