2. 外语
  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

admin2019-11-17  8
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 best describes the function of the last sentence of the passage?
选项 A、It points out that the events described in the passage may be atypical.
B、It alludes to the fact that there is disagreement in the scientific community over the importance of the Ordovician radiation.
C、It concludes that the evidence presented in the passage is insufficient to support the proposed hypothesis because it comes from a limited geographic area.
D、It warns the reader against seeing a connection between the biological and geologic changes described in the passage.
E、It alerts the reader that current knowledge cannot completely explain the relationship suggested by the evidence presented in the passage.
答案E
解析 Evaluation
The last sentence of the passage functions primarily to indicate that, though certain evidence from the geologic record suggests a possible cause of the Ordovician radiation, the current level of knowledge regarding the relationship between environmental factors and that radiation is not sufficient for a full understanding of that relationship.
A Although there may be certain geologic or evolutionary aspects of the Ordovician period that are atypical, the final sentence of the passage does not address them.
B Neither the final sentence nor the rest of the passage addresses any disagreements within the scientific community.
C Although the final sentence of the passage does indicate that current understanding of the relationship between the environmental factors discussed and the Ordovician radiation is incomplete, it does not indicate that it is because the evidence comes from a limited geographic area that the evidence is insufficient.
D The last sentence does not advise against seeing a connection between the biological and geologic changes discussed; it merely advises that such a connection is not yet fully understood.
E Correct. The last sentence indicates to the reader that current knowledge is insufficient for fully explaining the relationships among the evidence provided in the passage regarding geologic, ecological, and evolutionary changes.
The correct answer is E.
转载请注明原文地址:https://kaotiyun.com/show/MGkO777K
本试题收录于： GMAT VERBAL题库GMAT分类
0

GMAT VERBAL

GMAT

相关试题推荐
随机试题
最新回复(0)