Your network contains an Exchange Server 2010 server.You need to prevent a user named User1 from downloading attachments larger than 50 KB when using Exchange ActiveSync.Your solution must not affect other users.  What should you do first？（）

• A、Modify User1 Mailbox properties
• B、Create a New ActiveSync Mailbox Policy
• C、Create a New Exchange ActiveSync Mailbox policy
• D、Modify properties of Default Exchange ActiveSync Mailbox policy