
Explanation:
To meet the requirements for migrating DB1 to an Azure SQL Managed Instance, the following service tier and feature should be selected:
Service Tier - Business Critical
The Business Critical tier allows for read scale-out, enabling offloading of read-only workloads to secondary replicas. It also provides high availability with replication across multiple zones and support for up to 16 TB of storage. This ensures resiliency in case of a region outage, as needed in the solution.
Feature - Failover group
A Failover group provides automatic failover of a managed instance between different regions, ensuring that the solution remains available in the event of an Azure region outage. It supports geo-replication and enhances disaster recovery capabilities, which aligns with the resiliency requirement.