Your network contains one Exchange Server 2010 Client Access server named Server1.You have a user named User1.You need to limit the size of the attachments that User1 can download by using Exchange ActiveSync.The solution must not affect other users. What should you do first？（）

• A、Create new managed content settings.
• B、Modify the message size restrictions for User1.
• C、Create a new Exchange ActiveSync mailbox policy.
• D、Modify the default Exchange ActiveSync mailbox policy.