After App1 is migrated, you must implement a backup solution. Which resource should you create first?

The correct answer is Create a Recovery Services vault. A Recovery Services vault is a storage entity in Azure that houses data such as backups and replication points. It's the foundational component for implementing Azure Backup for various Azure resources, including virtual machines, SQL databases, and Azure file shares. Without a vault, you cannot configure backup policies or store backup data. Creating a recovery plan is part of Azure Site Recovery, which focuses on disaster recovery, not primary backup storage. Deploying an Azure Backup Server is for on-premises backups and isn't the first step for Azure-native resources. Creating a backup policy defines how backups are taken (frequency, retention), but it requires a vault to be created first to store these policies and the resulting backup data.