An internet is a combination of networks connected by （1）. When a datagram goes from a source to a （2）, it will probably pass many （3） until it reaches the routerattached to the destination network. A router receives a （4）from a network and passes it toanother network. A router is usually attached to several networks. When it receives a packet, towhich network should it pass the packet The decision is based on optimization: Which of theavailable（5） is the optimum pathway

（5）是（）

A.pathways

B.routers

C.diagrams

D.calls

方向继电器的作用是区分进路的性质和运行方向。