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The claim attributes increased publications to the grants. The strongest way to undermine a causal inference is to show preexisting differences that explain the outcome—selection bias. If grant recipients were already on faster publication trajectories, then post-grant differences could reflect prior momentum, not grant impact. Option B states this directly, severing the causal link. Option A is true in general but non-specific; field variation doesn’t show that these grants failed to cause the rise. Option C is irrelevant; website upgrades have no plausible mechanism for boosting publications. Option D might even support the mechanism (more help → more output), not weaken it. On GRE Argument tasks, the decisive weakening evidence usually identifies a confound aligned temporally and substantively with the claimed effect; here, prior trends among selected labs are exactly that confound.