You have an Exchange Server 2010 organization named contoso.com. Your company is investigating a user named User1. You need to prevent User1 from permanently deleting the items in his mailbox.  What should you run（）？ 

• A、Set-Mailbox User1 -LitigationHoldEnabled $true
• B、Set-Mailbox User1 -ModerationEnabled $true
• C、Set-Mailbox User1 -RetainDeletedItemsUntilBackup $true
• D、Set-Mailbox User1 -RetentionHoldEnabled $true