You work as the exchange administrator at TestKing.com. The TestKing.com network contains an Exchange Server 2003 Organization. The Exchange Server 2003 Organization contains a front end servernamed TESTKING-EX01 as well as a back end server named TESTKING-EX02 that is accessible fromthe Internet using mail.testking.com. TestKing.com wants to migrate the Exchange Server 2003 organization to Exchange Server 2010. You receive an instruction to deploy a Mailbox server named TESTKING-SR01 and a Client Access Servernamed TESTKING-SR02. Management also want all users to access Outlook Web Access and OutlookWeb App （OWA） using the https：//mail.testking.com URL. You need to determine the DNS configurationfor the external name of mail.testking.com. What should you do？（）