北回归线自东向西穿过我国的四个省（区）是（　　）

A．台湾、福建、广东、广西

B．台湾、福建、广东、云南

C．台湾、广东、广西、云南

D．台湾、福建、江西、广西

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

An internet is a combination of networks connected by （）.

A．modems

B．routers

C．switches

D．computers