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Q4~Q6: GWD32—32-34 The dry mountain ranges of the western United States contain rocks dating back 440 to 510 million years, to the Ordovician period, and teeming with evidence of tropical marine life. This rock record provides clues about one of the most significant radiations (periods when existing life-forms gave rise to variations that would eventually evolve into entirely new species) in the history of marine invertebrates. During this radiation the number of marine biological families increased greatly, and these families included species that would dominate the marine ecosystems of the area for the next 215 million years. Although the radiation spanned tens of millions of years, major changes in many species occurred during a geologically short time span within the radiation and, furthermore, appear to have occurred worldwide, suggesting that external events were major factors in the radiation. And, in fact, there is evidence of major ecological and geological changes during this period: the sea level dropped drastically and mountain ranges were formed, in this instance, rather than leading to large-scale extinctions, these kinds of environmental changes may have resulted in an enriched pattern of habitats and nutrients, which in turn gave rise to the Ordovician radiation. However, the actual relationship between these environmental factors and the diversification of life forms is not yet fully understood
Q4: The passage is primarily concerned with A. evaluating the evidence of a major geologic period and determining its duration B. describing an evolutionary phenomenon and speculating about its cause C. explaining the mechanisms through which marine life-forms evolved during a particular period D. analyzing the impact on later life-forms of an important evolutionary development E. contrasting a period of evolutionary change with other such periods --------------------------------------------------------------- Q5. Which of the following can be inferred from the passage regarding the geologic changes that occurred during Ordovician period? A. They were more drastic than those associated with other radiations B. They may have created conditions favorable to the evolution of many new life-forms C. They may have caused the extinction of many of the marine species living in shallow waters D. They may have been a factor in the development of new species adapted to living both on land and in water E. They hastened the formation of the extensive dry regions found in the western united states
我觉得两道题的答案应该都是B,可是答案是C和E. Q5: B能从文中灰色部分推出来。为什么会选E呢？ Q4: 文章中绿色部分suggesting,灰色部分的may have resulted都是作者在speculate原因。哪里有说进化的机制呢？ 请各位NN指点。 | 
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发表于 2008-3-13 17:36:00
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