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（4）处应选择（）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（）
Halloween originated as a celebration connected with evil spirits. Witches flying on broom sticks with black cats, ghosts, goblins (丑妖怪)and skeletons(骷髅) have all evolved as sym bols of Halloween. They are popular trick-or-treat costumes and decorations for greeting cards and windows. Black is one of the traditional Halloween colors, probably because Halloween festivals and traditions took place at night. In the weeks before October 31, Americans decorate windows of houses and schools with silhouettes of witches and black cats.
Pumpkins are also a symbol of Halloween. The pumpkin is an orange-colored squash, and orange has become the other traditional Halloween color. Carving pumpkins into jack-o’-lanterns is a Halloween custom also dating back to Ireland. A legend grew up about a man named Jack who was so stingy that he was not allowed into heaven when he died, because he was a miser. He couldn’t enter hell either because he had played jokes on the devil. As
A. black cats
B. goblins
C. fairs
D. skeletons
Networks can be interconnected by different devices. In the physical layer networks can be connected by (31) or hubs, which just move the bits from one network to an identical network. One layer up we find bridges and switches which operate at data link layer. They can accept (32) , examine the MAC address and forward the frames to a different network while doing minor protocol translation in the process. In network layer, we have routers that can connect two networks. If two networks have (33) network layer, the muter may be able to translate between the packer formats. In the transport layer we find transport gateway, which can interface between two transport connections. Finally, in the application layer, application gateways translate message (34) . As an example, gateways between Internet e-mail and X.400 e-mail must (35) the e-mail message and change various header fields.
（35）是（）我来回答:
