[外语类试卷]大学英语六级模拟试卷168及答案与解析.doc
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1、大学英语六级模拟试卷 168及答案与解析 一、 Part I Writing (30 minutes) 1 Directions: For this part, you are allowed thirty minutes to write a composition on the topic:“ What Do You Think of Challenge?“. You should write at least 150 words and you should base your composition on the outline ( given in Chinese) below: 1
2、. 挑战的意义; 2.如何迎接挑战; 3.我的看法 二、 Part II Reading Comprehension (Skimming and Scanning) (15 minutes) Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions attached to the passage. For questions 1-4, mark: Y (for YES) if the statement agrees with the in
3、formation given in the passage; N (for NO) if the statement contradicts the information given in the passage; NG (for NOT GIVEN) if the information is not given in the passage. 1 Part Reading Comprehension (Skimming and Scanning) Directions: In this part, you will have 15 minutes to go over the pass
4、age quickly and answer the questions on Answer Sheet 1. For questions 1-4, mark Y (for YES) if the statement agrees with the information given in the passage; N (for NO) if the statement contradicts the information given in the passage; NG (for NOT GIVRN) if the information is not given in the passa
5、ge. For questions 5-10, complete the sentences with the information given in the passage. Unity and Diversity Many physicists are engaged in the search for a “theory of everything“. Biologists, smugly, think they have found one already. Organisms that survive long enough to reproduce and are attract
6、ive enough to find a mate pass their genes on to the next generation. Those that do not are evolutionary cul-de-sacs. But the details how you go on from the basic principles of evolution to explain large-scale patterns in biology are more divisive. Scientific camps form. Their leaders step onto soap
7、 boxes. And only rarely do people concede that their own theories and those of their opponents are not always mutually exclusive. Since the early 1970s, the two grandest patterns of life how species are arranged in space and how they are arranged in time have divided their opposing camps quite neatl
8、y. Those who squabble over space disagree about why there are more species in the tropics than anywhere else. To them, the tropics are either where species are more often born (cradles of diversity) or where they tend not to die (museums of diversity). By contrast, biologists concerned with patterns
9、 in time tenaciously debate whether new species come into being in a smooth and gradual manner, or whether the history of life is actually a series of bursts of change that are interspersed with periods when nothing much happens. Two papers just published in Science have cast light on these question
10、s, and their findings, if not necessarily resulting in compromise, do show the value of taking leaves out of other peoples books. The “space biologists“ have looked into time, namely the fossil record over the past 11m years. Meanwhile the “time biologists“ have looked at the here and now and found
11、evidence in living species for periods of rapid evolution in their genes. Biological Spacetime The space biologists have the advantage that they agree about the pattern they are trying to explain. Almost all groups of life that have been studied be they fungi, plants, vertebrates or invertebrates, a
12、nd no matter whether they occur in forests, streams or seas seem to have more species the closer they are to the equator. To decide whether the tropics are a cradle or a museum, though, involves picking this pattern apart with statistics. And statistics work best when you have more than one sample.
13、That is the reason for reaching into the past. David Jablonski, of the University of Chicago, and his colleagues created their samples by dividing the past 11m years into three periods. For simplicitys sake, they also chopped the Earths surface into two: tropical regions and everywhere else, which t
14、hey called the “extratropics“. To avoid sampling bias, they restricted their analysis to one group of animals the bivalve molluscs that fossilise well. This allowed them to follow 431 “lineages“ of marine bivalve through the course of geological time. The vast majority of these lineages appear in th
15、e tropics and then spread into the extratropics, in other words, the tropics do, indeed, act as cradles of biodiversity. In fact, the pattern Dr Jablonski reports is probably more marked than his data suggest. That is because palaeontologists themselves are generally a temperate species and are most
16、 commonly found in the northern hemisphere. That means rocks in this region have been oversampled compared with those in the tropics. Also, tropical rocks tend to experience deep weathering, rarely poking above the ground as outcrops. That makes sampling them harder, even if you bother to look in th
17、e first place. The tropics do, indeed, act as cradles of biodiversity. Both of these facts mean it is likely that some lineages which seem to make their first appearance in the extratropical fossil record actually started out near the equator. The cradle hypothesis, then, looks strong. But that does
18、 not necessarily mean the museum hypothesis is wrong for, at the same time as the tropics were generating diversity they seem to have been preserving it as well. Although the bivalve lineages Dr Jablonski studied spread out from the equator in waves, they did not become extinct in the wake of these
19、waves. Instead of being forced out of tropical regions as they travelled poleward, they accumulated there. Common ground appears to be forming in time biology as well. The dispute is between the gradualists and those who think that the sudden shifts in fossil types seen in the geological record are
20、real, rather than a consequence of the irregular way that rocks are laid down. It got rather personal a few years ago, with references to evolution by creeps and evolution by jerks. But, in a similar way to Dr Jablonskis study, which suggests that models of cradles and museums present a false dichot
21、omy, a paper from a member of the gradualist camp of time biology endorses some features of jerky evolution. Some Jerks, Some Creeps Mark Pagel and his colleagues at the University of Reading, in England, reasoned that the theory of punctuated equilibria (the formal name given to evolution in bursts
22、) predicts a relation between the rate at which new species are formed and the rate of genetic change in an organisms recent past. A lineage that has spun off a lot of species will show more genetic change than one that has not. The alternative view, that evolutionary changes tick along gradually, s
23、uggests mutations would accumulate incrementally as time goes by, independently of how many new species a lineage spins off. Dr Pagel studied 122 family trees this way. He found that in about a third of them, there was more change in the DNA in those trees where more species had been generated. He a
24、lso found that punctuated evolution explained about 22% of such genetic changes, with the remainder unfolding smoothly through time. This means, among other things, that when biologists have calculated how long ago two lineages diverged by assuming change is regular, they may have their dates wrong.
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