You have an Exchange organization.All servers in the organization have Exchange Server 2010 Service Pack 1 （SP1） installed. You need to ensure that an administrator can recover hard-deleted e-mail messages from a user’s mailbox until the deleted item retention period has elapsed.All expired e-mail messages must be deleted when the retention period has elapsed. What should you do？（）

• A、From the Exchange Management Shell， run Set-MailboxDatabase -DumpsterStatistics $true.
• B、From the properties of the mailbox database， select the This database can be overwritten by a restore check box.
• C、From the Exchange Management Shell， run the New-MailboxSearch cmdlet.
• D、From the Exchange Management Shell， run the New-MailboxExportRequest cmdlet.
• E、From the properties of the mailbox， enable single item recovery.
• F、From the properties of the mailbox database， modify the Deletion Settings.