制度后评价的结果包含以下（）几类。

A.整体有效

B.有效但需优化

C.存在重大缺陷

D.失效

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（1）处应选择（）

A.modems

B.routers

C.switcher

D.computers