You are the network administrator for The network consists of asingle DNS domain named.You replace a UNIX server with a Windows Server 2003 computer namedTestKing1.TestKing1 is the DNS server and start authority (SOA) for testking.com. A UNIXserver named TestKing2 is the mail server for testking.com.You receive reports that Internet users cannot send e-mail to the testking.comdomain. The host addresses are shown in the following window.You need to ensure that Internet users can send e-mail to the testking.com domain.What should you do?（）
A. Add an _smtp service locator (SRV) DNS record for TestKing2.
B. Add a mail exchange (MX) DNS record for TestKing2.
C. Add an alias (CNAME) record for mail.testking.com.
D. Enable the SMTP service on TestKing1.
正确答案：参考B
