Sunflowers growing in pots were placed, with their roots submerged, in the pond contaminated with radioactive elements. The sunflowers kept growing; in the process, they absorbed radioactive elements. Within twelve days, 85 percent of the radioactive elements were removed from the water, which is no less than can be accomplished with the much more expensive conventional filtration techniques. Scientists therefore propose using sunflowers for decontamination wherever there are radioactively contaminated ponds.

Which of the following, if true, points to a limitation on the applicability of the proposed method of decontamination?

Some plants other than sunflowers can also remove radioactive elements from water. The water in many ponds contaminated with radioactive elements is so cold that it would kill sunflowers whose roots were submerged in it. Sunflowers that grow with their roots submerged in water grow less well than sunflowers growing under optimal conditions on dry land. Only species of sunflowers with large leaves can have their roots submerged in water and still keep growing. In ponds in which the circulation of the water is artificially increased, sunflowers absorb radioactive elements far faster than they do in other ponds.

答案是B

我想问一下，为什么不选D？

我觉得选B

D的话并不会对方法的适用性造成限制是对向日葵的选择造成限制

C的话是无关的，因为它长的好不好和它能不能减少辐射从题目中看不出来有联系