For each blank, choose the best answer from the four choices and write down on the answer sheet.
(21) is a six bytes OSI layer 2 address which is burned into every networking
device that provides its unique identity for point to point communication.
(22) is a professional organization of individuals in multiple professions which focuses on effort on lower-layer protocols.
(23) functions with two layers of protocols. It can connect networks of different speeds and can be adapted to an environment as it expands.
(24) is the popular LAN developed under the direction of the IEEE802.5.
(25) is the popular backbone technology for transmitting information at high speed with a high level of fault tolerance which is developed under the direction of ANSI.
（25）是（）
A.X.25
B.ATM
C.FDDI
D.SMDS
参考答案：C
解析：
MAC地址是6字节的OSI模型二层地址，它用来唯一标识提供点到点通信的设备；
IEEE是一个多领域的专门组织，他们致力于底层协议的制定；
网桥跟两层协议一起，连接两个不同速率的网络，能够适应不断扩展的网络环境；
令牌环是一种符合IEEES02.5标准的被广泛应用的网络；
FDDI是一种符合ANSI标准的高速信息传递骨干网技术，它具有很强的容错能力。