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 the 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 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 (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．reapers

B．relays

C．connectors

D．modems

儿童锁骨青枝骨折的治疗

A．手法复位+肩8字绷带固定4周B．不予固定治疗
C．手术切开复位+内固定
D．三角巾悬吊患肢3周
E．手法复位+小夹板固定