Critical Reasoning

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?

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

OA IS B

WHY IS D INCORRECT?

Sounds like a great plan: Use sunflowers to suck up the contamination. It worked in one pond, so why won't it work in others?

Answer (B) provides a clear, resounding answer: the sunflowers will die in most other ponds because the water is too cold. Dead sunflowers can't suck up the contaminants.

(D) only suggests we are limited in the type of sunflower we can use--the large leaved kind. Nowhere does in the argument does it state that these types of sunflowers are hard to find. So as long as we use the large leaved sunflower, we will be able to de-contaminate ponds.