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1. [多选题]As the Ezonexam network administrator, you are required to have a firm understanding of the OSI model. Why does the data communication industry use the layered OSI reference model? (Choose two)
A. It enables equipment from different vendors to use the same electronic components, thus saving research and development funds
B. It encourages industry standardization by defining what functions occur at each layer of the model
C. It divides the network communication process into smaller and simpler components; thus aiding component development, design and troubleshooting
D. It provides a means by which changes in functionality in one layer require changes in other layers
E. It supports the evolution of multiple competing standards and thus provides business opportunities for equipment manufacturers
2. [单选题]You have a class C network, and you need to design it for 5 usable subnets with each subnet handling a minimum of 18 hosts each. Which of the following network masks should you use?
A. 225.225.224.0.
B. 225.225.240.0.
C. 225.225.255.0.
D. 255.255.255.224
E. 225.225.255.240
3. [单选题]下列哪个network命令会告知此路由器开始使用IP地址为10.1.1.1、10.1.100.1和10.1.120.1的接口上的OSPF（）
A. network 10.0.0.0 255.0.0.0 area 0
B. network 10.0.0.0 0.255.255.255 area 0
C. network 10.0.0.1 0.0.0.255 area 0
D. network 10.0.0.1 0.0.255.255 area 0
4. [单选题]OSI七层模型中，“包”是哪一层数据封装的名称（）
A. 物理层
B. 数据链路层
C. 网络层
D. 传输层
5. [多选题]In which Spanning-Tree states does a switch port learn MAC addresses? (Select two)
A. Blocking
B. Listening
C. Forwarding
D. Learning
E. Relaying
