To ensure VMs running interdependent applications fail over one by one, as a group, the method to use is D: Failover plan. In Veeam Backup & Replication, a failover plan allows for the orchestration of a group of replicas to fail over in a predefined sequence. This includes the capability to set up delays between starting each VM, which is crucial for interdependent applications that must be started in a specific order to function correctly. The failover plan ensures that dependencies among the group are respected and that the startup sequence follows the correct order, enabling a smooth and organized transition to the failover state.