Networks can be interconnected by different devices in the physical layer networks can be connected by (1) 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 (2) examine the MAC address and forward the frames to a different network while doing minor protocol translation in the process in me network layer, we have routers that can connect two networks, If two networks have (3) 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 (4) . As an example, gateways between Internet e-mail and X.400 e-mail must (5) the e-mail message and change various header fields.

A．frimes

B．packets

C．packages

D．cells

保持乐观愉快的心态对我们身心健康、完成学业，以及将来的生活和工作都有很大的裨益。当你遇到下列情境时你会怎样做？为什么？

（1）为了备战期末考试，你紧张学习，但你发现效率非常低，甚至看到书本你都已非常烦恼了。

我会：___________________________________________________________________________

因为：___________________________________________________________________________

（2）你平时作文写得还好，但参加全县的“龙泉杯”作文比赛你却未能获奖。

我会：___________________________________________________________________________

因为：___________________________________________________________________________

（3）社区开展志愿者服务活动，主要帮助生活困难群众。

我会：___________________________________________________________________________

因为：___________________________________________________________________________