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09年MBA英语阅读理解与答案122
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In the following article, some sentences have been removed. For Questions 21-25, choose the most suitable one from the list A-G to fit into each of the numbered blank. There is one extra choice that does not fit in any of the gaps. Mark your answers on ANSWER SHEET 1. (10 points)
Between 5,000 million and 4,000 million years ago the Earth was formed. By 3,000 million years ago life had arisen and we have fossils of microscopic bacteria-like creatures to prove it. (21) . Nobody knows what happened, but theorists agree that the key was the spontaneous arising of self-replicating entities, i.e. something equivalent to "genes" in the general sense.
The atmosphere of the early Earth probably contained gases still abundant today on other planets in the solar system. Chemists have experimentally reconstructed these ancientconditions in the laboratory. If plausible gases are mixed in a flask with water, and energy is added by an electric discharge (simulated lightning), organic substances are spontaneously synthesized. These include the building blocks of RNA and DNA. It seems probable that something like this happened on the early Earth. Consequently, the sea would have become a "soup" of prebiological organic compounds. (22) .
Today the most famous selfreplicating molecule is DNA (deoxyribonucleic acid), but it is widely thought that DNA itself could not have been present at the origin of life because its replication is too dependent on support from specialized machinery, which could not have been available before evolution itself began. DNA has been described as a "hightech" molecule which probably arose some time after the origin of life itself. Perhaps the related molecule RNA, which still plays various vital roles in living cells, was the original self-replicating molecule. Or perhaps the primordial replicator was a different kind of molecule altogether. (23) . Variants that were particularly good at replication would automatically have come to predominate in the primeval soup. Varieties that did not replicate, or that did so inaccurately, would have become relatively less numerous. This led to ever-increasing efficiency among replicating molecules.
As the competition between replicating molecules warmed up, success must have gone to the ones that happened to hit upon special tricks or devices for their own self-preservation and their own rapid replication. The rest of evolution may be regarded as a continuation of the natural selection of replicator molecules, now called genes, by virtue of their capacity to build for themselves efficient devices (cells and multicellular bodies) for their own preservation and reproduction. (24) .
Fossils were not laid down on more than a small scale until the Cambrian era, nearly 600 million years ago. The first vertebrates may date back 530 million years, according to fossil evidence-primitive, jawless fishes with fins, gills, and fishlike muscle patterns-found in China in 1999. Vertebrates appear abundantly in fossil beds between 300 and 400 million years ago. (25) . Mammals and, later, birds, arose from two different branches of reptiles. The rapid divergence of mammals into the rich variety of types that we see today, from opossums to elephants, from anteaters to monkeys, seems to have been unleashed into the vacuum left by the catastrophic extinction of the dinosaurs, 65 million years ago.
Among vertebrates, the land was first colonized by lobe-finned and lung-bearing fish about 250 million years ago, then by amphibians and, in more thoroughgoing fashion, by various kinds of animals that we loosely lump together as "reptiles".
Once self-replicating molecules had been formed by chance, something like Darwinian natural selection could have begun: variation would have come into the population because of random errors in copying.
It is not enough, of course, that organic molecules appeared in the primeval soup. The crucial step, as noted above, was the origin of self-replicating molecules, molecules capable of copying themselves.
Although we naturally emphasize the evolution of our own kind-the vertebrates, the mammals, and the primates-these constitute only a small branch of the great tree of life.
When the environment changes, or when organisms move to a different environment, different variations are selected, leading eventually to different species. Harmful mutations usually die out quickly, so they don't interfere with the process of beneficial mutations accumulating.
Three thousand million years is a long time, and it seems to have been long enough to have produced such astonishingly complex contrivances as the vertebrate body and the insect body.
Some time between these two dates-independent molecular evidence suggests about 4,000 million years ago-that mysterious event, the origin of life, must have occurred.［748 words］
核心词汇
by/in virtue of 凭借（某种手段）；由于，因为 例：He was exempt from charges by virtue of his youth/of being so young.他因年幼而获得免费. / She became a British citizen by virtue of her marriage.她借助婚姻成了英国公民。
extinction n. ［U］ *①（物种）灭绝，绝种 例：be threatened with extinction濒临灭绝 ②（信仰、生活方式等）遭毁灭，消失，消亡
hit on/upon ① （经长时间考虑后）突然想出（好主意） 例：In this way we hit upon over 20 useful methods of work.就这样我们想出了20多种有用的工作方法。 *② 偶然发现（某物） 例： At last she hit upon a room that suited them nicely.最后她找到了一间适合他们使用的房间。
in more thoroughgoing fashion以更彻底的方式；in a... fashion以......方式 例：Leave the building in an orderly fashion.要有秩序地走出楼去。
interfere with *① 妨碍，打扰 例：Dont allow pleasure to interfere with duty.不要让娱乐妨碍了职责。 ② 干扰（广播或电视播送）
lay down ① 放下（武器等） 例：The general told the troops to lay down their arms.将军命令部队放下武器。 ② ［常用被动态］（正式地或坚决地）阐述，声明，规定 例：It is laid down that all applicants must sit a written exam.根据规定, 申请者一律需经笔试。 ③ 开始建造；开始做（奠基性的工作） 例：Crick and Watson laid down the foundations of modern genetic research.克里克和沃森为现代遗传学研究奠定了基础。 *④ (化石、地层等的)沉积形成
超纲词汇
anteater n.食蚁兽, 食蚁动物
contrivance n. *① 发明，发明物，发明的才能 ② 计谋，诡计
DNA 脱氧核糖核酸，deoxyribonucleic acid的缩写，指细胞核内携带基因信息的物质，具有双螺旋结构
gill n. *① 鱼鳃 ② （蘑菇或其他菌类的）菌褶
lobe ［ｌｕｂ］ n. *① （生物身体上的）肉垂，圆形的突出物 ② （=earlobe）耳垂 ③ （尤指脑、肺等的）叶
mutation n.（动物、植物的）突变，变异
opossum n. 尾有卷握力的小有袋动物，负鼠
primeval a. *① 太古的，太初的（地球或宇宙存在的最早期） ② 原始的，远古的 例：a primeval forest一片原始森林
primordial a. *① 太古的，太初的，自原始时代的 例：primordial soup原生浆液（地球上生命开始之前存在的物质、气体等混合物） ② 形式最简单的，基本的 例：primordial passions最基本的情感
RNA 核糖核酸，ribonucleic acid的缩写，指存在于生物细胞以及部分病毒、类病毒中的遗传信息载体，将DNA携带的遗传信息转移至蛋白质中，并参与其他细胞内的化学反应
Self-replicating a. 自我复制的
synthesized a. ① 组合的，综合的 *② 人工合成的
vertebrate n. 脊椎动物
长难句分析
Today the most famous selfreplicating molecule is DNA (deoxyribonucleic acid), but it is widely thought that DNA itself could not have been present at the origin of life because its replication is too dependent on support from specialized machinery, which could not have been available before evolution itself began.
该句是一个由but连接的并列句。前一个分句较简单，主干为The most famous selfreplicating molecule is DNA... 。后一个分句结构复杂，嵌套了多层从句，其主干是it is widely thought that...；it为形式主语，真主语是that引导的从句；because引导了一个较长的原因状语从句，其中又嵌套了which...非限定性定语从句做 machinery 的后置定语；from... 介词短语后置修饰support。
语篇分析
本文的选材领域是生命科学。作者介绍了自我复制分子在生命起源与动物进化中的重要作用。它是一篇事理说明文，大体按照时间顺序展开介绍。全文总计五段，可分成三大部分。
全文的写作顺序：第一至三段主要围绕生命起源的关键：自我复制分子展开介绍；第四段是过渡段，指出从自我复制分子到复杂生物体的出现，自然选择发挥了关键作用。第五段围绕脊椎动物的进化过程展开介绍。因此作者大体按照时间先后顺序安排全文内容。
一、第一至三段为第一部分，介绍生命起源的关键是自我复制分子的出现。
第一段内容概括：前三句利用时间线索从地球的形成（the Earth was formed）和生命的兴起（life had arisen），引出生命的起源（the origin of life）这一话题。第三句（［G］）起承上启下的作用，其中these two dates回指上文提到的两个时间；the origin of life与下文末句中的"关键是自我复制实体即基因的出现（the key was the spontaneous arising of selfreplicating entities）"在内容上相呼应。末句提出了全文论述的对象--自我复制实体。
连贯性：前三句句首的时间状语（分别为between 5,000 million and 4,000 million years ago, by 3,000 million years ago, some time between these two dates)相互呼应，是段内句子间连贯性的明显体现。
第二段内容概括：通过介绍生命起源的模拟实验，说明自我复制分子出现的条件。该段内容分为两个部分。第一部分是前四句，围绕"生命起源实验"展开论述。首句指出了进行实验的条件：原始地球大气中的气体现在仍然存在（the atmosphere of the early Earth contained gases still abundant today）。二至四句具体介绍化学家模拟原始大气状况进行生命起源的实验（reconstructed these ancient conditions in the laboratory），包括实验的材料（gases, water, energy）和结果（organic substances are synthesized）。第二部分是后四句，介绍自我复制分子的出现。第五、六句推理原始地球上出现了模拟实验中发生的情况（something like this happened on the early Earth）：原始海洋成为生命起源以前有机化合物汇集的地方（a "soup" of prebiological organic compounds）。第七、八句（［C］）转折指出，但更重要的不是有机分子的产生，而是自我复制分子的出现（the origin of selfreplicating molecules）。末句中的selfreplicating molecules与第一段末句中的selfreplicating entities是同一主题词的复现，达到语篇上下衔接。
连贯性：① 同义复现关系和代词的使用是段内连贯性的体现。同义词复现：early与ancient；organic substances、organic compounds和organic molecules；a soup of... 与the primeval soup。第四句中these指代上文提到的organic substances。② 本段末句中the crucial step、self-replicating molecules分别与第一段末句中的the key和selfreplicating entities是同义复现关系。跨越不同段落的同义复现关系是段落间连贯性的体现。③ 表假设的if是句内连贯性的体现。表结果的consequently是句与句之间的衔接手段。第七句承上启下，保证段内句子间的连贯性。末句引出下一段对自我复制分子起源的介绍，保证段与段之间的连贯性。 | 本文转自中英在职教育 |
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