You work as the enterprise exchange administrator at Xxx .The Xxx network consists of a domain named xxx .Xxx is using Microsoft Exchange Server 2010 as their messaging solution.You have to have the Application Identifier of xxx stored in a DNS record.The Application Identifier is used for the federated trust.What actions must you take on the DNS？（）

• A、You must set up recipient filtering.
• B、You must set up a Host （A）.
• C、You must use a TXT record.
• D、You must use a Pointer （PTR） record.
• E、You must use a Mail exchange （MX） record.