单选题 An internet is a combination of networks connected by 41 When a datagram(数据报) goes from a source to a 42 , it will probably pass many 43 until it reaches the router attached to the destination network. A router receives a 44 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 45 is the optimum pathway?