A new study indicates that residents of city X who frequently use public transportation report lower stress levels than those who primarily drive private vehicles. Therefore, encouraging more residents of city X to use public transportation will lead to a significant reduction in overall city stress levels.
✓ Correct Answer: Option A
The argument assumes that using public transportation *causes* lower stress. Option A eliminates an alternative cause (pre-existing traits) for the correlation, making the causal link assumed by the argument more likely.