2. 外语
  3. Prolonged and unseasonable frosts produce frost rings in deciduous trees, which grow in moderate climates. Frost rings do not ap

Prolonged and unseasonable frosts produce frost rings in deciduous trees, which grow in moderate climates. Frost rings do not ap

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问题 Prolonged and unseasonable frosts produce frost rings in deciduous trees, which grow in moderate climates. Frost rings do not appear in any of the fossilized deciduous trees that have been found in Antarctica. Hence, it is unlikely that such frosts occurred in Antarctica at the time the fossilized trees lived. Which of the following is an assumption on which the argument depends?
选项 A、There are fossilized nondeciduous trees from Antarctica that bear frost rings.
B、Deciduous trees are more likely to bear frost rings than are other tree varieties.
C、The process of fossilization does not completely obscure frost rings in deciduous trees.
D、Present-day deciduous trees are more sensitive to changes in temperature than were the deciduous trees of ancient Antarctica.
E、Prolonged and unseasonable frosts that might have occurred in Antarctica when the now-fossilized trees were still living did not always produce frost rings in deciduous trees.
答案C
解析 本题推理也是由一个事实“霜冻年轮没有出现在落叶树的化石中”，而得出一个解释性结论：“那时的南极洲的落叶树上没有霜冻”，属于典型的“B，A”型假设，思路应为“没有别的原因来导致B”。如果形成化石的过程使得落叶树中的霜冻年轮完全模糊，那么也就从另外一个角度解释了为什么“霜冻年轮没有出现在落叶树的化石中”，因此上面的解释性结论必然不对。所以(C)是一个使结论成立的必需条件，因此(C)是正确答案。(A)、(B)、(C)均为无关选项；(E)易误选，但(E)中的“not always”表明了(E)起到了部分支持作用。
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