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 pattem 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 AND:(C) 我想了好久 还是想不通 这题我选(B) 我看兔大和tnt24这题答案都是写(C) 实在是想不通 感觉原文里没有讲mechanism 应该是讲说整个过程 而且机制吧 且後面 一段写出这个推论可能还不完备 感觉更符合了(B)的答案 感觉就是(C)的范围较小 且我看不出机制在哪 请大大给予我指点!!! 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 ANS:(E) 这题我也选(B) 想了好久 一样想不通 原文说geologic changes的确有加快了地形的产生 但是 那也只有写出说地形上升 并没有说dry region阿...就感觉如果是(E)的话有点过度推论 因为只有讲说有助於地形上升 但是并没有讲说广阔的dry region形成 而且感觉原文里 面讲得就是说此种geologic changes会导致许多新生命的进化 感觉还是(B) 囧rz... 我看这段定位的 these kinds of environmental changes may have resulted in an enriched pattem of habitats and nutrients, which in turn gave rise to the Ordovician radiation 可是看tnt24和兔大的24答案也是(E) 真的好困惑 完全想不通 请大大们指导 THX --

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