When starting an on-demand lab from backup files for mission-critical VMs, the appropriate SureBackup feature to configure is A: Application Group. An Application Group in Veeam Backup
& Replication is a predefined group of VMs that are started together in the SureBackup job. This feature is designed to ensure that interdependent VMs, such as those comprising a multi-tier application, are started in a sequence that respects their operational dependencies, allowing for comprehensive verification and testing. The Application Group can include the mission-critical VMs and any associated VMs required for the application environment to function correctly, ensuring that all components are available and interact as expected within the isolated on- demand lab environment. This setup facilitates effective testing or troubleshooting in a manner that closely mirrors the production environment without impacting live operations.

A backup proxy is responsible for transferring data from the source to the backup repository, while the cache repository stores temporary data during backup processes. By deploying these components on a dedicated backup network, you can isolate backup traffic from the main production network, reducing potential congestion and increasing the overall performance of the backup job.

Explanation
https://helpcenter.veeam.com/docs/agentforwindows/userguide/backup_job_mode.html?ver=60

Veeam Backup & Replication allows you to set up failover plans to control the order in which VMs are started during a failover. By creating a failover plan, you can specify that the database servers boot before the application servers. This is achieved by setting up VM dependencies within the failover plan, ensuring that the database servers (which are critical for the application servers to function) are operational before the application servers start. Creating a disaster recovery template (B), creating a replica mapping (C), or initiating a planned failover (D) does not directly address the boot order of the servers during failover.

Explanation
Refer tohttps://helpcenter.veeam.com/docs/backup/vsphere/backup_proxy.html?ver=100