A city implemented a new rapid transit line. In the year following its opening, traffic congestion decreased by 15%, and air quality improved by 10%. A city official claimed the new transit line significantly improved both traffic and environmental conditions. Which of the following, if true, would most weaken the official's claim regarding the transit line's impact?
✓ Correct Answer: Option B
If neighboring cities without the transit line saw similar improvements, it suggests a broader, regional factor (e.g., economic downturn, weather) is responsible, not the transit line itself. This directly challenges the claim of the transit line's specific impact.