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To undermine a causal claim, present a credible alternative explanation tied closely to the measured outcome. Option A shows that the increase is limited to customers targeted by a concurrent coupon mailer, a separate intervention that plausibly explains repeat purchases. If true, this co-movement compromises the attribution to the app. Option B (satisfaction) is orthogonal to causality; users might like the app without it driving behavior. Option C is background context about competitors and timing; it doesn’t address whether our increase was caused by our app. Option D (overall traffic up 2%) is weak and nonspecific; the outcome at issue is repeat purchases, not footfall. On GRE Argument weaken questions, the strongest rebuttals identify confounds temporally aligned with the effect and specific to the population in which the effect appears, thereby severing the cause–effect link.