2. 外语
  3. In the passage, the author is primarily interested in______ It can be inferred from the passage that calcium carbonate shells__

In the passage, the author is primarily interested in______ It can be inferred from the passage that calcium carbonate shells__

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问题 In the passage, the author is primarily interested in______
It can be inferred from the passage that calcium carbonate shells______
选项 A、are not as susceptible to deterioration as rocks
B、are less common in sediments formed during an ice age
C、are found only in areas that were once covered by land ice
D、contain radioactive material that can be used to determine a sediment’s isotopic composition
E、reflect the isotopic composition of the water at the time the shells were formed
答案E
解析 E is the best answer. Lines 29-33 of the passage state that the calcium carbonate shells of marine organisms are constructed with “oxygen atoms drawn from the surrounding ocean.” This water contains varying proportions of oxygen 16 and oxygen 18 and, according to the passage, “becomes progressively enriched in oxygen 18”with the onset of an ice age (lines 19-27). The author states that “The degree of enrichment can be determined by analyzing ocean sediments…composed of calcium carbonate shells of marine organisms (lines 27-31)”. Thus, it can be inferred that the shells of marine organisms would reflect the isotopic composition of the surrounding ocean water at the time when the shells were formed.
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