Practice GMAT Critical Reasoning Question

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As a result of implementing an experimental farming system that combined aggressive new fertilization, deep irrigation, and speculative pesticides, the yield on crops at a farm in central California grew consistently and considerably over the past six years. However, yields this year unexpectedly plummeted, causing the farm's owners considerable financial difficulties.

Which of the following statements, if true, best explains the unexpected drop in yield?

A)	As a result of a serious and recent economic recession, the market for the products the farm produced shrank in size during the past year.
B)	Other farms that began using the experimental system at about the same time also reported an unexpected plummet in yields this year.
C)	The central California region where the farm in question is located experienced a drought 9 years ago, 3 years ago, and this past year.
D)	A different experimental system, used on a different crop, failed after two years at a farm in Iowa. Scientists later discovered that chemicals involved in this different system slowly poisoned the soil.
E)	Significant and sustained increases in agricultural productivity eventually lead to an exhaustion of important nutrients in land.

Correct Answer: E

The yield at a central Californian farm dropped significantly after 6 years of consistent growth. Clearly, something of importance to the yield changed. Some possibilities include: (1) a storm decimated the crop (although this level of storm could have only hit this year, as the crops grew "consistently and considerably over the past six years") (2) the farmer stopped using the technique (3) over a period of six years, the technique overused natural soil nutrients and drained important chemicals that the farm crops needed to grow.

The original argument pertains to a decline in the yield of the farm, not a decline in the buyers. The farm's yield has no relationship with the number of buyers as yield simply refers to the ratio of seeds planted to crops available for harvest.
Although this confirms that the drop the farm in central California experienced is not unique, it does not explain the drop in yield.
Since a drought occurred 9 years ago prior to the experimental system and during the experimental system (3 years ago) without any affect on yields, it is not logical to conclude that the drought caused the decline in yields this year. In other words, since the yield grew "consistently" even during the drought 3 years ago and 6 years ago, it is illogical to conclude that the drought caused the decline in yield this year.
The circumstances between the two experimental systems are too different to allow comparisons and a logical deduction that the errors of the Iowa system explain the errors of the central California system. Specifically: (1) the length of time before declines in yields occurred differed considerably (2) the crops the farm produced differed (3) the geographic region of the farm (and climate) differed considerably.
The sustained (6 years, "consistently") and significant ("considerably") expansion in productivity ("yield") led to exhaustion of nutrients, meaning crops could not attain the chemical compounds they needed to grow. This answer explains why the crop yield dropped after so many years and why it dropped after years of growth.

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