Rainwater contains hydrogen of a heavy form called deuterium. The deuterium content of wood reflects the deuterium content of rainwater available to trees during their growth. Wood from trees that grew between 16,000 and 24,000 years ago in North America contains significantly more deuterium than wood from trees growing today. But water trapped in several North American caves that formed during that same early period contains significantly less deuterium than rainwater in North America contains today.

Which of the following, if true, most helps to reconcile the two findings?


There is little deuterium in the North American caves other than the deuterium in the water trapped there.

Exposure to water after a tree has died does not change the deuterium content of the wood.

Industrialization in North America over the past 100 years has altered the deuterium content of rain.

Trees draw on shallow groundwater from rain that falls during their growth, whereas water trapped in caves may have fallen as rainwater thousands of years before the caves formed.

Wood with a high deuterium content is no more likely to remain preserved for long periods than is wood with a low deuterium content.

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情景：雨水中含有一种叫deuterium的物质。木头中含有的deuterium反映了树木在生长的过程中吸收的雨水中的deuterium。16,000 到24,000之前的树木比今天的树木中含有更多的deuterium。但是，山洞中的水的情况是完全相反的。

推理：本题是一个“现象解释型考题”。按照正常逻辑来说，结论为“山洞中16,000 到24,000之前的水中含有deuterium的量要比今天的水的情况要多”。由于前提和结论描述的是相同的内容，所以本题为类比推理。推理结构为：
前提：16,000 到24,000之前的树木比今天的树木中含有更多的deuterium
结论：16,000 到24,000之前的水比今天的水中含有更多的deuterium

选题方式：类比推理一共具有两个评估方向，简而言之，即，要么提到“树木”或“水”，要么给出与这两个案例相平行等价的案例C。

选项分析：

A选项：北美山洞中的deuterium含量和山洞里水的deuterium含量是不同的。本选项没有论述树木和山洞水的区别，而是在论述山洞和水的区别。

B选项：树木死后对水的接触不会改变木头中含有的deuterium的量。本选项只讲了树木的情况，没有讲到山洞水的情况。

C选项：北美的工业在过去100年改变了雨中deuterium的含量。本选项没有提及两个类比的对象。

D选项：Correct. 树木吸收的是浅层的来自于雨水的地表水，但是山洞中的水可能来自于在山洞形成的数千年以前的雨水。显然地，本选项论述了两个类比对象的区别。

E选项：高含量deuterium的木头不会比低含量的更可能保存的时间更长。本选项只讲了树木的情况，没有讲到山洞水的情况。

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