The variance test for Evaluate questions. The credited answer is the question whose two possible answers swing the conclusion in opposite directions; a question whose answers both leave the conclusion standing is a trap. The managers' conclusion is causal: the self-checkout lanes, by cutting wait times, caused the 12 percent sales rise at these eight stores. The data is a before-and-after comparison of the same eight stores over the same window, so the open gap is whether some other change at those stores over those same three months could independently explain the rise.
(B) is correct. Run the variance test. If a competing grocery store near the eight stores closed during those months, displaced shoppers would flow to Brightleaf and sales would rise regardless of self-checkout, so the managers' causal claim is undercut. If no nearby competitor closed, that alternative cause is removed and the self-checkout attribution holds up better. Opposite answers move the conclusion in opposite directions, which is exactly what a useful evaluation question must do.
(A) is on-topic but conclusion-inert: whether the lanes were easy to use does not tell us whether they, as opposed to an outside factor, produced the rise; sales already rose either way. It is tempting because it is the obvious thing to ask about self-checkout, but it is the wrong thing to ask about the cause. (C) is a forward-looking decoy: a plan to expand the rollout is irrelevant to what caused an increase that has already occurred. (D) is the strongest distractor, a wrong-comparison near-miss: it looks like a rigorous comparison, but chains that skipped self-checkout differ on many dimensions, so a smaller or larger rise among them cannot isolate self-checkout as the cause at Brightleaf's specific stores; the conclusion does not cleanly swing on it. (E) confuses cost with cause: how often the machines needed repair bears on the expense of operating them, not on whether they drove sales. Only (B) opens and closes an alternative cause for the rise at the same stores over the same window, so its answer most affects whether the conclusion holds.