GWD 19-19 求助！！！

aeolusero二

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.

答案选D，可我觉得B也可以削弱啊~~~~
碰到GWD我真是不会了。。。请教各位！！！

aeolusero二

哦~~谢谢~~~理解了~~
可是为什么选D我也不太懂，能不能麻烦再解释一下啊？、
谢啦~~~~

starry1008

The hypothesis is: this shortage of iron prevents plankton from thriving.

Note the word SHORTAGE, which denotes a relative value.

Then look at choice B) Certain areas of the ocean support an abundance of plankton despite having particularly low concentrations of iron.

Here LOW does not equal a SHORTAGE. A low concentration of iron might just be sufficient for the organisms to survive.