Situation: A study involving two aisles painted differently is cited as evidence that bright colors increase retail sales.
Reasoning: This is a typical experiment, meaning we ask the typical question of experiments: were the samples fair and representative? To strengthen this argument, we need to demonstrate either that the differences between the aisles are limited to color, or that the effects on this store are representative of all stores.
Choice (B) matches this prediction. By ruling out many potential sources of bias, it makes it far more likely that color scheme is in fact the cause of the discrepancy found by the experimenters.
Choice (A) might trap students who assume that store brands are hard to sell. If they are hard to sell, then it would be even more impressive that the color aisle had boosted sales. However, in poorer neighborhoods or during economic recessions, it might be the premium brands that suffer. Since this answer choice indicated a difference between aisles, it's actually a weakener.
Choice (C) is also distracting, since it seems to imply that the two aisles are similar. However, the two inventories differ, even if they are both a mix of price ranges. If one was selling fruit while the other sold paper goods, any comparison between them would be invalid.
Choice (D) suggests that the effects of the study are unique to that particular store, which weakens the generalization of the results.
Choice (E) is a clear weakener, since it would imply that the brightly colored aisle had an advantage based on placement within the store.
The correct answer is (B).