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  3. The dry mountain ranges of the western United States contain rocks dating back 440 to 510 million years, to the Ordovician perio

The dry mountain ranges of the western United States contain rocks dating back 440 to 510 million years, to the Ordovician perio

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问题 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. 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.
Which of the following can be inferred from the passage regarding the geologic changes that occurred during the Ordovician period?
选项 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 lan d and in water.
E、They hastened the formation of the extensive dry regions found in the western United States.
答案B
解析 Inference
The question asks what can be inferred from the passage’s claims regarding the geologic changes that took place during the Ordovician period. The passage indicates that during this period the sea level dropped and mountain ranges were formed and that these changes, rather than leading to large-scale extinctions, may have created more favorable habitats providing greater nutrients, which would likely have been favorable to newly evolved life-forms.
A The passage does not mention other radiations and does not compare the Ordovician geologic changes to geologic changes associated with other radiations.
B Correct. The passage does suggest that certain geologic changes that occurred during the Ordovician period may have created conditions favorable to the new life-forms associated with the Ordovician radiation.
C The passage does not indicate whether any marine species became extinct; in fact, it explicitly denies that the geologic changes led to any large-scale extinctions.
D The passage does not indicate that any new species were adapted to living both on land and in water. It merely discusses marine life-forms.
E Although these geologic changes did likely create newly dry areas in the western United States, it does not indicate that these areas are extensive.
The correct answer is B.
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