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问题 单项选择题

长期处于在振动和噪声环境下的工人，蛋白质代谢特点是（）。

A.分解代谢降低，出现负氮平衡

B.分解代谢加强，出现负氮平衡

C.分解代谢加强，出现正氮平衡

D.合成代谢降低，出现正氮平衡

E.合成代谢加强，出现正氮平衡

答案

参考答案：B

单项选择题 A1/A2型题

下述肺野划分标准，哪项是错误的（）

A.肺门位于中肺野内带

B.由内向外，肺野被分为内带、外带

C.第2肋骨前端下缘水平线以上为上肺野

D.第4肋骨前端下缘水平线以上为中肺野

E.第4肋骨前端下缘水平线以下为下肺野
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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 （66） 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 （67） , 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 （68） network layer, the router may be able to translate between the packet 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 （69） . As an example, gateways between Internet e-mail and X.400 e-mail must （70） the e-mail message and change various header fields.

（67）处填（）。

A．frames

B．packets

C．packages

D．cells
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