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