单项选择题

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

it will probably pass many （） until it reaches the router attached to the destination network．

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