Passage Summary: Researchers found that people who went through a trauma (but stayed mentally healthy) have higher stress hormones than people who never had a trauma, leading them to believe the trauma changed their body chemistry.

Conclusion: Experiencing a traumatic event can cause changes in the amount of cortisol a person produces when stressed.

Reasoning: People who have faced trauma but did not develop PTSD show higher cortisol levels under stress than those who have never experienced trauma.

Analysis: This argument suffers from a correlation-versus-causation error. The author observes a difference in cortisol levels and assumes the trauma caused it. However, it is equally possible that the high cortisol levels existed *before* the trauma and actually acted as a protective factor that prevented these individuals from developing PTSD. To weaken the argument, look for an answer that suggests this alternative causal path—that the hormone levels explain why they didn't get PTSD, rather than the trauma explaining the hormone levels.