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问题 单项选择题

利HSI切入VOR径向方位，在切入过程中，判断飞机回到预定方位的时机（）。

A.航道偏离杆随飞机运动而回中，说明飞机回到预定方位

B.航道偏离杆随飞机运动而远离中心不动时，飞机回到预定方位

C.航道偏离杆运动情况不定，无法进行判断

答案

参考答案：A

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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单项选择题 案例分析题

某一防冻剂进行检测，所测数据列于下表，计算这一防冻剂的性能指标并回答下述问题。（混凝土一次拌和30L，混凝土容重为2400kg/m3，负温温度为-10℃）

则掺该防冻剂混凝土的负温养护7d再转标准养护56d的抗压强度比R-7+56为（）。

A.121%

B.120%

C.119%

D.118%
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