You work as the enterprise exchange administrator at Xxx .The Xxx network consists of a domain named xxx . Xxx has three Exchange Server 2007 mail servers named XXX-EX01， XXX-EX02 and XXX-EX03 that has the following implementation： records.What action must you take to make sure of the availability of the mailboxes on XXX-EX03 if the employees utilize the Exchange ActiveSync after the instrallation of XXX-EX04？（）

• A、You should use Basic authentication on Exchange ActiveSync and set up only Basic authentication on the RPC virtual directory.
• B、You should use NTLM authentication on the RPC virtual directory.
• C、You should use Microsoft Challenge Handshake Authentication Protocol version 2 （MS-CHAP v2） on XXX-EX01.
• D、You should use the anonymous setting in the authentication type for the Microsoft-Server-ActiveSync virtual directory on XXX-EX01.