Use Transactional Replication.
When you can't afford to remove your SQL Server database from production while the migration is occurring, you can use SQL Server transactional replication as your migration solution.
Note: There are two primary methods for migrating a SQL Server 2005 or later database to Azure SQL Database. The first method (database copy or BACPAC importation) is simpler but requires some, possibly substantial, downtime during the migration. The second method (transactional replication) is more complex, but substantially eliminates downtime during the migration.
Incorrect:
Not D: The import BACPAC method includes downtime during migration.
Reference:
https://docs.microsoft.com/en-us/azure/azure-sql/database/migrate-to-database-from-sql-server#method-1-migration-with-downtime-during-the-migration