The essence of(74) is the invention of a hierarchical, domain-based naming schemE.It is primarily used for mapping host names and e-mail destinations to IP addresses.
A.DNS
B.NNTP
C.CDP
D.FTP
A.A.DNS
B.NNTP
C.CDP
【参考答案】
A
解析:参考译文:DNS的本质是一个基于域的命名方案,它主要用来把主机名称和电子邮件的日的地址映射为IP地址。