题目内容：
根据下列题干，回答题：Networks can be interconnected by different devices in the physical layer networks can be con- nected 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 ad- dress 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, applica- tion 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.
请选择（ 1 ）处最佳答案
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