TT系统多用于供电可靠性要求很高的电气装置中。（）

An internet is a combination of networks connected by (1). When a datagram goes from a source to a  (2), it will probably pass many (3) until it reaches the router attached to the destination network. A router receives a  (4) 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 (5) is the optimum pathway?

空白（3）处应选择（）

A.destinations

B.routers

C.packets

D.computers