问题 单项选择题

以下关于路由选择协议相关技术的描述中,正确的是()。

A.通常,路由信息协议的跳数小于等于16,比较适用于小型的、动态的网络环境

B.当运行RIP的路由器刚启动时,初始(V, D)表中各路由的距离均为∝

C.最短路径优先协议是使用路由矢量的内部网关协议,其主干区域ID为0(或0.0.0.0)

D.OSPF规定每隔一段时间要刷新一次数据库中的链路状态,以确保链路状态数据库与全网的状态保持一致

答案

参考答案:D

解析:

[考点透解] 路由信息协议(RIP)是一种分布式、基于向量一距离(V-D)的动态路由选择协议,其特点是算法简单、易于实现。其“跳数(Hop count)”一般小于等于15,等于16时定义为无穷大。据此,选项A的说法有误。 当运行路由信息协议(RIP)的路由器刚启动时,对其(V,D)路由表进行初始化。初始化的路由器只包含所有与该路由器直接相连的网络的路由。由于是直接相连的网络,不需要经过中间路由器的转接,因此初始(V,D)表中各路由的距离均为0。据此,选项B的说法有误。 最短路径优先协议(OSPF)最主要的特征是使用分布式链路状态协议(Link State Protocol)。据此,选项C的说法有误。 为了适应规模很大的网络,OSPF协议通过划分区域来提高路由更新收敛速度。每个OSPF区域拥有一个32位的区域标识符(用点分十进制或十进制整数表示)。区域ID为0(或0.0.0.0)表示骨干区域。 在基于OSPF协议的网络运行过程中,只要一个路由器的链路状态发生变化,该路由器就要使用链路状态更新分组向全网更新链路状态。为了确保链路状态数据库与全网的状态保持一致,OSPF规定每隔一段时间(例如30分钟)要刷新一次数据库中的链路状态。据此,选项D的说法正确。

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The National Gallery

Description:

The National Gallery is the British national art museum built on the north side of Trafalgar Square in London. It houses a diverse collection of more than 2,300 examples of European art ranging from 13th-century religious paintings to more modern ones by Renoir and Van Gogh. The older collections of the gallery are reached through the main entrance while the more modern works in the East Wing are most easily reached from Trafalgar Square by a ground floor entrance.

Layout:

The modern Sainsbury Wing on the western side of the building houses 13th- to 15th-century paintings, and artists include Duccio, Uccello, Van Eyck, Lippi, Mantegna, Botticelli and Memling.

The main West Wing houses 16th-century paintings, and artists include Leonardo da Vinci, Cranach, Michelangelo, Raphael, Bruegel, Bronzino, Titan and Veronese. 

The North Wing houses 17th-century paintings, and artists include Caravaggio, Rubens, Poussin, Van Dyck, Velazquez, Claude and Vermeer. 

The East Wing houses 18th- to early 20th-century paintings, and artists include Canaletto, Goya, Turner, Constable, Renoir and Van Gogh. 

Opening Hours:  The Gallery is open every day from 10am to 6pm (Fridays 10am to 9pm) and is free, but charges apply to some special exhibitions. 

Getting There:  Nearest underground stations: Charing Cross (2-minute walk), Leicester Square (3-minute walk), Embankment (7-minute walk), and Piccadilly Circus (8-minute walk). 

小题1:In which century’s collection can you see religious paintings?

A.The 13th.

B.The 17th.

C.The 18th.

D.The 20th.小题2: Where are Leonardo da Vinci’s works shown?

A.In the East Wing.

B.In the main West Wing.

C.In the Sainsbury Wing.

D.In the North Wing.小题3:Which underground station is closest to the National Gallery?

A.Piccadilly Circus

B.Leicester Square

C.Embankment

D.Charing Cross