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Difficulty: HardStrengthen

Agronomist: The crop yields of farms in the Delta region have increased by 20 percent since a new soil-aeration technique was introduced three years ago. The developer of this technique claims that it improves nutrient absorption, directly causing the surge in yields. However, this claim is incorrect; the true cause of the increased yields is the unusually favorable rainfall pattern the Delta region has experienced over the same three-year period.

Which of the following, if true, provides the strongest evidence to support the agronomist's conclusion?

  1. Farms in the neighboring Echo region, which experienced the exact same favorable rainfall patterns but did not adopt the new soil-aeration technique, also saw a 20 percent increase in crop yields over the last three years.Answer
  2. B
    Under controlled greenhouse conditions with identical watering schedules, plants grown using the new soil-aeration technique produced significantly higher yields than plants grown in standard soil.
  3. C
    The developer of the soil-aeration technique was recently discovered to have exaggerated the benefits of a completely different agricultural tool in a previous marketing campaign.
  4. D
    Over the last three years, the percentage of farms in the Delta region using the new technique increased rapidly, but the absolute number of acres dedicated to farming decreased.
  5. E
    Historical data from the Delta region shows that past decades with high average crop yields were consistently correlated with periods of heavy investment in agricultural technology.

Answer

The correct answer is the option stating that farms in the neighboring Echo region experienced the exact same favorable rainfall patterns but did not adopt the new soil-aeration technique, and still saw a 20 percent increase in crop yields.
The agronomist claims that favorable rainfall, rather than a newly introduced soil-aeration technique, caused a 20 percent increase in crop yields. This is a classic causal argument where two potential causes occurred at the same time. The correct answer provides a perfect control scenario: a neighboring region that experienced the exact same rainfall but did NOT use the new technique. Because this control region also experienced the identical 20 percent yield increase, it strongly supports the conclusion that the rainfall alone is sufficient to cause the surge, effectively isolating it as the true variable.

Step-by-Step Solution

1
Identify the main conclusion and the premises of the argument.
The main conclusion is that unusually favorable rainfall caused the 20 percent increase in crop yields. The premises are that yields increased after the introduction of a new aeration technique, but favorable rainfall also occurred concurrently.
Evaluating an argument requires a precise understanding of the causal claim the author is attempting to prove.
2
Analyze the logical gap in the agronomist's reasoning.
The agronomist asserts that rainfall, rather than the aeration technique, caused the yield increase, but provides no evidence to definitively separate the effects of these two simultaneous variables.
Identifying the missing link allows you to determine what specific evidence is needed to strengthen the argument.
3
Evaluate the options to find one that isolates the agronomist's proposed cause.
The correct option demonstrates that in a comparable region where only the rainfall occurred (without the aeration technique), the exact same yield increase resulted.
In causal reasoning, showing a 'cause without effect' or an 'effect without the rival cause' (a control group) is the most robust way to strengthen a specific causal hypothesis.

Key Concept

Strengthening Causal Arguments via Control Groups
Estimated Time:1m 45s
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