In a Cisco NAM high-availability configuration, when does the secondary Cisco NAM take over?

A.
When the timeout value is exceeded during data-mirroring activities

B.
When the IP-based heartbeat signal fails to be transmitted and received within a certain time period

C.
When the UDP heartbeat signal fails to be transmitted on the serial heartbeat connection between failover peers

D.
When the UDP heartbeat signal is not transmitted and received within a certain time period