Final answer:
If a primary HA device stops replying to heartbeat signals, the secondary device is designed to automatically take over, ensuring continuous service availability without interruption.
Step-by-step explanation:
When a primary HA (High Availability) device stops replying to heartbeat signals, the correct response is B) Secondary device takes over. This process is a crucial part of a high availability setup where two or more devices are configured to provide continuous services. The heartbeat is a signal sent between devices in a cluster to monitor each other's status. If a primary device stops sending a heartbeat, indicating a potential failure or outage, the secondary device assumes control to maintain service availability without user interruption or data loss. This automatic failover is designed to provide resilience and reliability within computing environments.