Critical Reasoning

gmat_dec wrote:Which of the following most logically completes the argument?
Pluxtonica thrives in soil with high concentrations of chlorides that are toxic to most other plants. Plant scientists quoted in 'Journal of herbs' that Pluxtonica produces large amounts of Proline, an amino acid that, in experimental conditions, renders these chlorides chemically inert. Possibly, therefore, the herb's high Proline production is what allows it to grow in chloride -rich soils, a hypothesis that would gain support if ______.

Cause : Proline production
Effect : Allows pluxtonica to grow


A. the herb's high level of proline production is found to be associated with an unusually low level of production of other amino acids
Incorrect : This does not affect the causal relationship in any way.

B. proline is found in all parts of the plant-roots, stem, leaves, and flowers
Incorrect : Just because proline is found in 'ALL PARTS' of the plant does not support the hypothesis that it allows the plant to 'GROW'

C. cultivation of the herb in soil with high concentrations of the chlorides will, over an extended period, make the soil suitable for plants to which the metals are toxic
Incorrect : This actually weakens the hypothesis by implying that 'adaptability' to chlorides make the plant grow.

D. others of the closely related group of plants are also found to produce proline in large quantities
Incorrect : Discussion about other closely related group of plants is irrelevant here.

E. the concentration of proline in the growing herb declines as the plant approaches maturity
Correct : This is what we are looking for. The passage says proline lets the plant 'GROW'. This statement says when the plant approaches maturity (stops growing) the concentration of proline declines. Hence it supports the hypothesis by stating that when the cause (proline production) does not happen..the effect (growth of plutonica) does not happen.