[单项选择]Communication networks can be classified in terms of their physical arrangement or (74) . Three common (74) are the star, bus, and ring.
A. structures
B. topologies
C. protocols
D. frames

[单项选择]Communication networks can be classified in terms of their physical arrangement or (74) . Three common (74) are the star, bus, and ring.
A. structures
B. topologies
C. protocols
D. frames

[单项选择]Framing a problem in mythological terms can point toward solutions at deeper mythic levels. For centuries, the guiding myth of Western culture has been what might be called the "Grand Narrative of Progress. " It is the story of movement toward a goal— achievement, improvement, and conquest. Modern science and technology have propelled this myth, extending the human life-span, harnessing natural resources and the power of the atom, carrying sounds through the atmosphere, and exploring outer space by defying gravity itself. Rational thought and the empirical scientific method became the chief instruments of the progress myth, and they promised to discern which economic system, which form of government, and which aesthetic design would best lead humanity out of confusion toward a utopian future. As science tests hypotheses, those that fail to be verified are abandoned, allowing science to move forward in a self-correcting, progressive direction. Mythology was equated w
A. myth is very important in the problem-solution relationship
B. science and technology are helpful to solve the problems
C. the Grand Narrative of Progress is powerful
D. problem and solution are the twins

[单项选择]

Networks can be interconnected by different devices. In the physical layer, networks can be connected by (11) or hubs, which just move the bits from one network to an identical network. One layer up we find bridges and switches, which operate at data link layer. They can accept (12) ,examine the MAC address, and forward the frames to a different network while doing minor protocol translation in the process. In the network layer, we have routers that can connect two networks. If two networks have (13) network layer, the router may be able to translate between the packer formats. In the transport layer we find transport gateway, which can interface between two transport connections. Finally, in the application layer, application gateways translate message (14) . As an example, gateways between Internet e-mail and X.400 e-mail must (15) the e-mail message and change various header fields.

12（）
A. frames
B. packets
C. packages
D. cells