You have an Exchange Server 2010 organization that contains a single Mailbox server.The Mailbox server contains two mailbox databases named DB1 and DB2.You need to restore a backup of DB1.Users must be able to connect to their mailboxes on DB1 during the restore process.What should you create first？（）

• A、a database availability group （DAG）
• B、a Client Access server array
• C、a Recovery Mailbox database
• D、a recovery storage group