GWD 19-19 逻辑请教！

regansun

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.

对于答案D没有问题，但是选项A我认为也是能可以的呀，A的字面意思我没理解错的话就是并不是所有的nitrogen compounds  是 plankton 所需要的nutrient，也就是说，原文里的实验把iron compounds 加入后仍然没有达到预期效果的原因实际是因为实验中的 此 nitrogen compounds 并非 彼 nitrogen compounds  不也可以吗？

regansun

你这么一说似乎真的这么一回事，他因的话应该关联性上面更近或者更直接一点才可以 非常感谢！

hartmann

我明白你得理解，但A还是不对：

A说了有一些nitrogen compounds  不是 plankton 所需要的nutrient，但是，A无法证明那次release iron实验环境中的 nitrogen compounds 就是那些compounds。

如果A改为： 有一些nitrogen compounds 不是 plankton 所需要的nutrient，而且，那次实验正好在含有这些compounds的海水中进行的；那么，实验的不成功，就可以通过nitrogen compound来解释。这样，A就是对的。

regansun

不好意思打错了，答案是D，我明白虽然讨论的是iron，可是通过他因削弱或者他因增强不也是GMAT常考的一种方式吗？

比如有些逻辑题在要你增强论点A是导致B的原因的时候，可以通过排除是其他原因导致B来增强A就是导致B的原因

sdcar2010

The answer is D, not C.

Focus on the conclusion, which discusses IRON not nitrgen or other nutrients for plankton.