Critical Reasoning (CR) | Re: Studies have shown that highway drivers are less likely to d

The correct answer is (B). If signs of civilization make highway drivers more likely to obey the speed limit, then (B) provides further. A plowed field, unlike a field of wild flowers is evidence of civilization, and if also this causes drivers to obey the speed limit, that's independent confirmation for the psychologist argument, a good strengthener.

The argument explicitly says it is equalizing for car & road & traffic conditions, so that nullifies choices (A) & (C).

Choice (D)
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