请教这道逻辑狗上的意思和思路啊？

beatG

是GWD的题，文章意思大概懂，但不明白问题到底是问什么的啊？小弟阅读一向一般，请路人好人强人给点帮助啊，帮忙翻译和讲解下思路啊。。谢谢


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. (Answer)
E.    The iron compounds released into the area occur naturally in areas of the ocean where plankton thrive.

BoraBora

应该是这样理解的吧：段落的第一句说浮游生物生活在海水表面，所以尽管倒入了很多铁， 但是如果洋流很快把那些富含铁的水从海水表面移走，浮游生物也就不能增多了。我觉得比较快的是抓关键词吧： 第一句说Plankton live near the surface; D答案说displace iron from the surface.