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问题 单项选择题

报警及监控系统是利用现代（），对可能发生的抢劫、火灾等紧急情况，能够（手动）自动现场报警，并将警情自动传送到报警中心的一种技术设施。

A、计算机技术

B、信息技术

C、电子探测技术

D、遥感技术

答案

参考答案：C

选择题

恐龙和翼龙非常繁盛的时期是[ ]

A．古元代

B．古生代

C．新生代

D．中生代

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单项选择题

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
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