To enable writing to a storage account, the one has to be configured first. Storage accounts are containers used to store Azure Storage objects, including blobs, files, tables, etc, for the auditing needs, general-purpose standard storage accounts will support storing audit data trail, to learn more about storage accounts.
Incorrect:
Not A, Not C: Use a storage account in the same region as the managed instance to avoid cross-region reads/writes.
Reference:
https://www.sqlshack.com/getting-started-with-azure-sql-database-auditing-using-blob-storage/
https://docs.microsoft.com/en-us/azure/azure-sql/managed-instance/auditing-configure
