问题 填空题

交换机的工作原理与透明网桥极为相似,它们都通过一种( )的方法,自动地建立和维护一个记录着目的MAC地址与设备端口映射关系的地址查询表。

答案

参考答案:自学习

解析: 这道题考察交换机的基本工作原理。交换机的工作原理与透明网桥极为相似,它们都通过一种自学习的方法,自动地建立和维护一个记录着目的MAC地址与设备端口映射关系的地址查询表,即交换表。当交换机启动并开始工作后,在转发每一个数据帧时,都会根据帧中的目的MAC地址,通过查询交换表来决定把数据帧转发到交换机的哪一个端口,或者直接将帧丢弃。

解答题
阅读理解

Do you know why different animals or pests (昆虫) have their special colors? Colors in them seem to be used mainly to protect themselves.

  Some birds like eating locusts (蝗虫), but birds cannot easily catch them. Why? It is because locusts change their colors together with the change of the colors of crops(庄稼). When crops are green, locusts look green. But as the harvest time comes, locusts change to the same brown color as crops have. Some other pests with different colors from plants are easily found and eaten by others. So they have to hide themselves for lives and appear only at night.

If you study the animal life, you’ll find the main use of coloring is to protect themselves. Bears, lions and other animals move quietly through forests. They cannot be easily seen by hunters (猎人). This is because they have the colors much like the trees.

Have you ever noticed an even stranger act? A kind of fish in the sea can send out a kind of very black liquid (液体)when it faces danger. While the liquid spreads over (散开), its enemies (敌人)cannot find it. And it immediately swims away. So it has lived up to now though it is not strong at all.

小题1:From the passage we learn that locusts________.

A.are small animals

B.are easily found by birds

C.are dangerous to their enemies

D.change their colors to protect themselves小题2:How can pests with different colors from plants keep out of danger?

A.They run away quickly.

B.They have the colors much like their enemies.

C.They hide themselves by day and appear at night.

D.They have to move quietly.小题3:Bears and lions can keep safe because _________.

A.they have the colors much like the trees

B.they move quietly

C.they like brown and gray colors

D.they live in forests小题4:Why can the kind of fish live up to now?

A.Because it is very and strong.

B.Because the liquid it sends out can help it escape from its enemies.

C.Because the liquid it sends out can kill its enemies.

D.Because it swims faster than any other fish.小题5:Which is the best title for this passage?

A.The Change of Colors for Animals and Pests

B.Colors of Different Animals and Pests

C.The Main Use of Colors for Animals and Pests

D.Some Animals and Pests