2016-05-23更新GMAT逻辑机经
3. 海洋上富含氮物质的地方有种海藻
CR：记得有道GWD的题，讲一般海洋上富含氮物质的都有一种藻，然而有个地方没这种藻。科学家觉得这个地方少盐所以没藻。于是他们撒了很多盐，当还是没藻。
【整理君】
Plankton generally thrive in areas of the ocean with sufficient concentrations of certain nitrogen compounds near the surface, where plankton live. Nevertheless, some areas, though rich in these nitrogen compounds, have few plankton. These areas have particularly low concentrations of iron, and oceanographers hypothesize that this shortage of iron prevents plankton from thriving. However, an experimental release of iron compounds into one such area failed to produce a thriving plankton population, even though local iron concentrations increased immediately.
Which of the following, if true, argues most strongly against concluding, on the basis of the information above, that the oceanographers’ hypothesis is false?
A. Not all of the nitrogen compounds that are sometimes found in relatively high concentrations in the oceans are nutrients for plankton.
B. Certain areas of the ocean support an abundance of plankton despite having particularly low concentrations of iron.
C. The release of the iron compounds did not increase the supply of nitrogen compounds in the area.
D.A few days after the iron compounds were released, ocean currents displaced the iron-rich water from the surface.
E.The iron compounds released into the area occur naturally in areas of the ocean where plankton thrive.
【分析】
第一句话等于说了high nitrogen compunds→more plankton;
第二句话等于说了high nitrogen compounds→few plankton。
前两句话的意思等于说了nitrogen compounds跟plankton没有直接关系。所以，第三句才推测：few plankton→ low iron(A→B)。至此，果因推理出现了。为了question这个果因推理，一个实验被设计，貌似找到了few plankton且high iron(A且非B)的结果。如果该实验结果为真，则的确可以有效削弱第三句话中的果因推理。问：argue against concluding that hypothesis is false 变成人话就是 support hypothesis。要找选项可以support hypothesis或者weaken experiment。
A和C说的是nitrogen compounds，我们要找的是plankton和iron的关系。则AC错。
B说的是 more plankton→low iron，也就是 非A→B，这是“有因无果”的削弱，削弱了A→B的果因推理：无因果关系。
D. 有效的质疑了experiment，证明发生的并不是 few plankton且high iron(A且非B)，而是few plankton→low iron(A→B)。所以是加强。
E.说的是iron release into the area of ocean where plankton thrive.可根据题干第二句these area...low iron...prevent plankton from thriving.和第三句 an experiment release of iron into one such area...也就是做实验的area本来就是few plankton的area. E选项直接否定了前提的内容!所以，E必错。
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