An internet is a combination of networks connected by (26) ．When a datagram goes from a source to a (27) ，it will probably pass many (28) until it reaches the router attached to the destination network．A router receives a (29) 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 (30) is the optimum pathway

A．user

B．host

C．city

D．destination