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.
When a datagram goes from a source to a （）
A．user
B．host
C．city
D．destination
