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.