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A trial of a catalyst measured the yield of a chemical reaction at twenty plants that adopted the catalyst and reported that average yield rose afterward. To strengthen the claim that the catalyst raised yield, which of the following, if true, would be most helpful?
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Correct answer
A
Strengthen: the claim is that the catalyst raised yield, so the gap is whether yield would have risen anyway.
(A) closes it with a control, comparable plants without the catalyst saw no rise, isolating the catalyst as the cause. (B) cites the supplier's reputation, not evidence of effect. (C) is a reporting requirement. (D) concerns cost. (E) names expectation, which leaves rival causes open rather than ruling them out.
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