问题 填空题

如果路由表中没有包含到某一特定网络或特定主机的路由,路由选择例程就可以将数据报发送到______上。

答案

参考答案:默认路由

解析:

[分析]: 默认路由是一个特殊的路由,当路由表中找不到目标路由时,就将数据报转发到该默认路由。

单项选择题

阅读下面短文,回答文后问题。

据明人蒋一葵《长安客话》记述,昔日的永乐大钟,日供六僧击之,“昼夜撞击,声闻数十里,其声宏宏,时远时近,有异他钟”。如此美妙绝伦的钟声是怎么样形成的呢

从外表上可以明显看出,大钟的钟壁上下厚度不同,钟腰的厚度是94毫米,而钟口的壁厚是185毫米。测音表明,不同厚度的各个部分,都会产生相应的频率振动,发出不同的声音,而这众多分音的汇集就是一首雄伟的交响曲。

加上永乐大钟合理的合金成分比率,优雅钟声的出现就不是偶然了。明永乐大钟的成分中含铜 80.5%、锡16.4%及少量其他元素。当含锡在16%左右时,就能保证钟体强度、韧度适度,保持钟声振动的持续性;若含锡量过多或太少都会使钟声余音减短,那么就无法欣赏到永乐大钟闻声数十里的悠长钟声了。

同时还发现,永乐大钟的正下方,由一个直径4米、深0.7米的八角形地坑,它不单方便人们仰视大钟内壁,还有为钟声散音的功能,与现代舞台前乐池的声学作用异曲同工。

三管齐下方才造就了永乐大钟举世无双的完美音质。那么,明朝的能工巧匠是如何设计出这令人叫绝的声场呢

中国古钟千百年来的发展脉络有其自成一派的风格样式。中国钟的基本形状是钟声高度与口径之比在 1:0.7左右,西洋中则在1:1左右。中国钟用钟杵从外壁敲击,而西洋钟用钟舌从内部敲击,因而发出的声音比中国钟更加急促、高昂。

通过物理分析,钟声产生于撞钟引起的振动,而钟声的强弱、高低、音色主要取决于钟体的形状和材质。钟壁厚则钟声沉闷,反之清脆;钟体短而口径大则钟声消失得比较快,反之悠长。永乐大钟上端闭塞、下端钟口开放,形成钟顶小、钟腰细、钟身长、钟口外张似喇叭。当撞击时,引起钟声振动,使各分音的频率恰当,产生拍频现象。此外,成分分析的结果告示我们,永乐大钟的合金成分比率与《周礼·考工记》中的“六齐”大致相符。

根据本文,大钟下方地坑的声学作用是()。

A.方便撞钟材

B.方便观赏

C.汇聚分音

D.钟声散音

单项选择题

A new golden age of cartography has suddenly dawned, everywhere. We can all be mapmakers now, navigating across a landscape of ideas that the cartographers of the past could never have imagined. Maps were once the preserve of an elite, an expression of power, control and, latterly, of minute scientific measurement. Today map-making has been democratised by the internet, where digital technology is spawning an astonishing array of maps, reflecting an infinite variety of interests and concerns, some beautiful, some political and some extremely odd. If the Budget has made you feel gloomy, you can log on to a map that will tell you just how depressed you and the rest of the world are feeling. For more than two years, the makers of wefeelfine, org have harvested feelings from a wide variety of personal blogs and then projected these on to the globe. How happy are they in Happy Valley How grim is Grimsby You can find out.
Where maps once described mountains, forests and rivers, now they depict the contours of human existence from quite different perspectives: maps showing the incidence of UFOs, speed cameras or the density of doctors in any part of the world. A remarkable new map reflects global telephone usage as it happens, starkly illustrating the technological gap between, say, New York and Nairobi. Almost any measurable human activity can be projected, using a computer "mash-up". A new online map called whoissick, org allows American hypochondriacs to track who is ill with what and where at any given moment. A hilarious disclaimer adds. "whoissick is not intended to be a substitute for professional medical advice. " The new generation of amateur map-makers are doing for the traditional atlas what Wikipedia has already done to the encyclopaedia, adding layers of new information, some fascinating and useful, much that is pointless and misleading, and almost all from personal perspectives.
The new digital geography marks a return to an earlier form of cartography, when maps were designed to reveal the world through a particular prism. The earliest maps each told a story framed by politics, culture and belief. Ancient Greeks painted maps depicting unknown lands and strange creatures beyond the known world. Early Christian maps placed Jerusalem at the middle of the world. British imperial maps showed the great advance of pink colonialism spreading outwards from our tiny islands at the centre.
Maps were used to settle scores and score points, just as they are today. When Jesuit map-makers drew up a chart of the Moon’s surface in 1651, craters named after heretical scientists such as Copernicus and Galileo were dumped in the Sea of Storms, while more acceptable thinkers were allowed to float in the Sea of Tranquility. The 19th century heralded a more scientific approach to map-making; much of the artistry and symbolism was stripped away to create a two-dimensional representation of three-dimensional reality. Maps became much more accurate, but less imaginative and culturally revealing.
The boom in amateur mapping, by contrast, marks a return to the earlier way of imagining the world when maps were used to tell stories and impose ideas, to interpret the world and not simply to describe its physical character. New maps showing how to avoid surveillance cameras, or the routes taken by CIA planes carrying terrorist suspects on "extraordinary rendition", are political statements rather then geographical descriptions.
The earliest maps were also philosophical guides. They showed what was important and what was peripheral and what might be imagined beyond the edges of the known. A stunning tapestry map of the Midlands made around the time of Shakespeare and recently rediscovered, depicts forests, churches and the houses of the most powerful families, yet not a single road. It does not purport to show a physical landscape, but a mental one. Maps have always tried to show where we are, literally or philosophically. The explosion of online mapping, however, offers something even broader, a set of maps that combine to express individual personality.
Oscar Wilde wrote that "a map of the world that does not include Utopia is not worth even glancing at, for it leaves out the one country at which Humanity is always landing. And when Humanity lands there, it looks out, and, seeing a better country, sets sail. " If Utopia means knowing where you fit in your own world—knowing how many UFOs hover above you, how much graffiti has appeared overnight, how happy your next-door neighbour is and whether he is likely to have picked up anything contagious—then humanity may finally have a map showing how to get there.

The word "preserve" in the sentence "Maps were once the preserve of an elite" (para. 1) can best be paraphrased as ______.

A.unique preservation

B.privileged right

C.exclusive enjoyment

D.advantageous activity