剑桥雅思9阅读：Test3雅思阅读PASSAGE3真题+答案+解析

　　Passage3

　　Information Theory — the Big Idea

　　lnformation theory lies at the heart of everything-from DVD players and the genetic code of DNA to the physics of the universe at its most fundamental. lt has been central to the development of the science of communication, which enables data to be sent electronically and has therefore had a major impact on our lives.

　　A In April 2002 an event took place which demonstrated one of the many applications of information theory. The space probe, Voyager I, launched in 1977, had sent backspectacular images of Jupiter and Saturn and then soared out of the Solar System on a one-way mission to the stars. After 25 years of exposure to the freezing temperatures of deep space, the probe was beginning to show its age. Sensors and circuits were on the brink of failing and NASA experts realised that they had to do something or lose contact with their probe forever. The solution was to get a message to Voyager I to instruct it to use spares to change the failing parts. With the probe 12 billion kilometres from Earth, this was not an easy task. By means of a radio dish belonging to NASA's Deep Space Network, the message was sent out into the depths of space. Even travelling at the speed of light, it took over 11 hours to reach its target, far beyond the orbit of Pluto.Yet, incredibly, the little probe managed to hear the faint call from its home planet, and successfully made the switchover.

　　B It was the longest-distance repair job in history, and atriumph for the NASA engineers. But it also highlighted the astonishing power of the techniques developed by American communications engineer Claude Shannon, who had died just a year earlier. Born in 1916 in Petoskey, Michigan, Shannon showed an early talent for maths and for building gadgets, and made breakthroughs in the foundations of computer technology when still a student.While at Bell Laboratories, Shannon developed information theory, but shunned the resulting acclaim. In the 1940s, he single-handedly created an entire science of communication which has since inveigled its way into a host of applications, from DVDs to satellitecommunications to bar codes - any area, in short, where data has to be conveyed rapidly yet accurately.

　　C This all seems light years away from the down-to-earth uses Shannon originally had for his work, which began when he was a 22-year-old graduate engineering student at the prestigious Massachusetts Institute of Technology in 1939. He set out with an apparently simple aim: to pin down the precise meaning of the concept of 'information’.The most basic form of information, Shannon argued, is whether something is true or false - which can be captured in the binary unit, or 'bit', of the form 1 or 0. Having identified this fundamental unit, Shannon set about defining otherwise vague ideas about information and how to transmit it from place to place.In the process he discovered something surprising: it is always possible to guarantee information will get through randominterference – ‘noise’, - intact.

　　D Noise usually means unwanted sounds which interfere with genuine information. Information theory generalises this idea via theorems that capture the effects of noise with mathematical precision. In particular, Shannon showed that noise sets a limit on the rate at which information can pass along communication channels while remaining error-free. This rate depends on the relative strengths of the signal and noise travelling down the communication channel, and on its capacity (its ‘bandwidth’). The resulting limit, given in units of bits per second, is the absolute maximum rate of error-free communication given signal strength and noise level. The trick, Shannon showed, is to find ways of packaging up – ‘coding’, - information to cope with the ravages of noise, while staying within the information-carrying capacity -'bandwidth* - of the communication system being used.

　　E Over the years scientists have devised many such coding methods, and they have proved crucial in many technological feats. The Voyager spacecraft transmitted data using codes which added one extra bit for every single bit of information; the result was an error rate of just one bit in 10,000 - and stunningly clear pictures of the planets. Other codes have become part of everyday life - such as the Universal Product Code, or bar code, which uses a simple error-detecting system that ensures supermarket check-out lasers can read the price even on, say, a crumpled bag of crisps. As recently as 1993, engineers made a major breakthrough by discovering so-called turbo codes - which come very close to Shannon's ultimate limit for the maximum rate that data can be transmitted reliably, and now play a key role in the mobilevideophone revolution.

　　F Shannon also laid the foundations of more efficient ways of storing information, by stripping out superfluous(‘redundant’) bits from data which contributed little real information. As mobile phone text messages like ‘I CN C U’ show, it is often possible to leave out a lot of data without losing much meaning. As with error correction, however, there’s a limit beyond which messages become tooambiguous. Shannon showed how to calculate this limit, opening the way to the design of compression methods that cram maximum information into the minimum space.

　　Question 27 ：

　　答案： D

　　关键词： factors, affecting, transmission of information

　　定位原文：D 段 2、3、4 句“Information theory generalizes…”通过用精确的数学计算得出 噪声影响的定理，信息理论概括出了上述这个观点。Shannon 特别指出，噪声决定了信息通过信道无误差传送的极限速度。这个速度取决于信号与噪声在信道中传送时的相对强度以及信道传送数据的能力。

　　解题思路： 题干中的 affecting 对应原文中的 depend on，题干中的 factors 对应原文中的 noise 和 communication channel。这道题目相对较难，不太容易理解。从表面上看这个题目要求，似乎每段都可能包含一个信息。但其实可以使用排除法，很快地排除其他段落后，在 D 段中查找起来就更有针对性。

　　Question 28 ：

　　答案： F

　　关键词： unnecessary information, omitted

　　定位原文：F 段第 1、2 句“Shannon also laid the foundations…” 通过去除含有较少真实信息的多余数据，Shannon 也为开发更有效率地存储信息的方式奠定了基础。正如手机短信“I CN C U”(I can see you 的缩写) 一样，往往在省略数据之后，意思基本保持不变。

　　解题思路：题干中的 unnecessary 和 omitted 分别对应原文中的 superfluous‘( redundant’) 和 stripping out, leave out。

　　Question 29 ：

　　答案： B

　　关键词： Shannon’s attitude

　　定位原文：B 段第 4 句“While at Bell Laboratories, Shannon…”

　　解题思路：在贝尔实验室时，Shannon 发展了信息理论，但他并不看重因此而获得的荣誉。原文中的这处细节，对应了问题中 Shannon 对于名声的态度。

　　Question 30 ：

　　答案： E

　　关键词： machine, capable, incomplete information

　　定位原文：E 段第 3 句“Other codes have become…” 其他一些编码已经成为了 我们日常生活的一部分，比如通用商品代码或称条形码。这些编码都使用了一个简单的纠错系统，确保超市的扫码器能够读出甚至是在一个弄皱了的薯条袋上的价格。

　　解题思路：题目中的 machine 对应原文中 supermarket check-out lasers，题目中的 incomplete information 对应原文中 the price on a crumpled bag of crisps，薯条包装袋被弄皱了，上面的条形码显示就不会太清晰，因此此处理解为不完整信息。

　　Question 31：

　　答案： A

　　关键词： incident, information theory

　　定位原文： A 段第 1 句和最后一句，“In April 2002 an event took…” “Yet, incredibly, the little…” 2002 年 4 月发生的一件事展现了 信息理 论的一大应用。……然而令人难以置信的是，这颗小小的探测器成功接收到了来自故乡星球微弱的召唤，并顺利地更换了零件。

　　解题思路：题目中 incident 的英文解释为“an event, especially one that is unusual or important”，对应原文中的 event; 而题干中的 information theory 对应原文中的 information theory。事实上，A 段整个段落都是对这个细节事件的描述。

　　Question 32：

　　答案： C

　　关键词： initially intended to, achieve 定位原文： C 段前两句“This all seems light…”

　　解题思路： 1939 年，22 岁的 Shannon 是著 名的麻省理工学院工程系的研究生，那时候通信科学的实际应用似乎遥不可及，与当时 他在研究工作中实际使用的技术相差很远。他从一个再简单不过的目标开始着手——确 定“信息”的准确概念。题目中的 initially intended to 对应原文 set out with an apparently simple aim。

　　Question 33：

　　答案： Jupiter Saturn(in either order)

　　关键词： both... and, probe transmitted pictures

　　定位原文： A 段第 2 句“The space probe, Voyager I…”

　　解题思路： 两个空格之间有表示并列关系的连接词 both... and...,可预测要填的两个词为并列关系的名词。通过定位词 pictures 找到原文中包含 images 的那句话，pictures 和 images 为同义转述。很明 显 images 后面的一组并列关系的名词 Jupiter 和 Saturn 就是正确答案。

　　Question 34：

　　答案： Solar System

　　关键词： then left the

　　定位原文：同上题

　　解题思路：空格前为定冠词 the,因此预测出空格处应该 填名词，并且此词在和定位词 then left the 意思相近的表达后面。因此，我们可以很轻松地定位到原文中 and then soared out of..., left 和 soared out of 是同义转述，后面的 Solar System 即为正确答案。

　　Question 35：

　　答案： sensors circuits(in either order)

　　关键词： both...and…, freezing temperatures, scientists

　　定位原文： A 段第 4 句“After 25 years of exposure to…”

　　解题思路： 两个空格之间有表示并列关系的连接词 both...and...，可以预测要填的两个词为并列关系的名词。通过定位词 freezing temperatures 定位到原文中的原词。按照顺序原则继续往下找，定位词 scientists 对应原文中的 NASA experts。仔细读包含这两个定位词的两句话，很明显存在一组并列关系的名词 sensors and circuits。然后进一步推敲答案的确定性。题干中的 stop working 对应原文中的 on the brink of failing, 从而可以最终确定 sensors 和 circuits 为正确答案。

　　Question 36：

　　答案： spares

　　关键词： probe, replace, distance, difficult

　　定位原文： A 段第 4 句“The solution was to get a message to Voyager I to…”

　　解题思路： 空格前为介词 with,可预测空格里应该填名词，并且此词在 distance 之前。题干中的 distance 定位到原文中 12 billion kilometers from Earth, 题干中的 difficult 定位到原文中 this was not an easy task, 因此需要从前一个句子中找答案。题干中 replace 对应原文中 change, 题干中的 replace them with 对应原文 中的 use spares to change the failing parts, 显然， spares 为正确答案。

　　Question 37：

　　答案： radio dish

　　关键词： transmit, message, speed of light

　　定位原文： A 段倒数第 3 句“By means of a radio dish…”

　　解题思路：空格前为冠词 a，可以预测空格处应该填辅音开头的名词。用定位词 speed of light 定位到原文中，transmit 与原文中的 send out 属于同义转 换。message 是如何以光速传送出去的呢?题 干中的...was used to 对应于原文中的 by means of..., 因此 radio dish 为正确答案。

　　Question 38：

　　答案： TRUE

　　关键词： true or false, was the starting point, over distances 定位原文： C 段第 3 句“The most basic form of…” Shannon 认为最基本的信息形式是判断事物正确与否，这可以用二进制单位“比特”以 1 或者 0 的形式记录。解题思路：本题解题关键是 Shannon 研究远距离传送信息的起点。原文陈述，Shannon 认为最基本的信息形式是判断事物正确与否。starting point = basic form, 题干与原文完全一致。

　　Question 39：

　　答案： TRUE

　　关键词： signal strength, noise level,

　　定位原文： D 段第 4 句“This rate depends on…”

　　解题思路： 这个速度取决于信号与噪音在信道中传送时的相对强度以及信道传送数据的能力(即带宽)。题干中判断的关键点 is determined with, 与原文 depends on 表述一致。

　　Question 40：

　　答案： FALSE

　　关键词： now, Shannon, convey information

　　定位原文： E 段最后一句“As recently as 1993，engineers made a major…” 就在最近的 1993 年，工程师们取得了一项重大突破，发现了所谓的 Turbo 码，这与 Shannon 提出的信息可以安全传送的最 大速度极限接近。现在，Turbo 码在移动可视电话变革中起着关键的作用。

　　解题思路： 将题干中的 now 对应到原文的 as recently as 1993 以及后面的 now,题干中要判断的关键点是 more...than Shannon had anticipated...(超过 Shannon 预期)，与原文中的...which come very dose to Shannon’s ultimate limit (与 Shannon 提出的最 大限度接近)。题干与原文所述事实不符合。