B. It is a network layer protocol that resolves addresses
C. It is a session layer API that makes remote procedures transparent to a user
D. It is a transport layer function for unreliable transport
20) Ping sends an ICMP echo command to an IP address in order to determine whether anetwork connection exists to that node (Ping向一个I P地址发送了一个I C M P回送命令,目的是确定是否存在到那个节点的网络连接)?
A. True B. False
21) Which of the following best describes TCP/IP (下面的哪句话最准确地说明了T C P / I P )?
A. A static protocol
B. A proprietary protocol