Passage Summary: Researchers compared people doing cardio versus lifting weights; after a stressful math test, the cardio group was less physically stressed, leading researchers to credit aerobic exercise for stress management.

Conclusion: Aerobic exercise is effective at assisting the body in managing psychological stress.

Reasoning: In a study, participants in aerobics classes showed lower physical stress symptoms after a difficult math task compared to those in weight-training classes.

Analysis: The argument jumps from a correlation (the aerobics group had fewer symptoms) to a causal claim (aerobics caused the improvement). To make this stick, we must assume that the groups were comparable from the start. If the aerobics group was naturally more relaxed or better at math before the experiment even began, the results wouldn't necessarily prove anything about the exercise itself. Look for an answer that ensures the two groups didn't have pre-existing differences in their stress responses.