A recent study found that people who engage in at least 30 minutes of physical exercise daily tend to have lower stress levels compared to those who do not exercise. Based on this, a fitness trainer concluded that regular exercise directly reduces stress levels.

Which of the following assumptions underlies the fitness trainer's conclusion?

The correct assumption underlying the fitness trainer's conclusion is Option D, "The study's results are reliable and accurately represent the relationship between exercise and stress."

This is because the trainer's conclusion that regular exercise directly reduces stress levels depends on the assumption that the study's findings are valid and correctly reflect a cause-and-effect relationship between exercise and stress. Without trusting the reliability of the study, the conclusion cannot hold.

Option A suggests reverse causation (that people with lower stress levels are more likely to exercise), which goes against the trainer’s claim that exercise reduces stress.

Option B focuses on exercise being the primary factor for stress reduction, but it doesn’t address the underlying assumption that the study itself is valid.

Option C implies that no other factors contribute to stress reduction, which is unnecessary for the trainer’s conclusion. The trainer only needs to assume that exercise plays a significant role.

Option E adds a detail about the timeframe for stress reduction, but the trainer’s conclusion isn’t dependent on whether the effect is short- or long-term.

The trainer’s conclusion rests on the belief that the study is trustworthy and accurately captures the link between exercise and stress, which makes Option D the best choice.