Passage Summary: People who tackle problems head-on have healthier gums than those who ignore their problems. Since stress weakens the immune system, the author believes this explains why the 'avoiders' have more gum issues.

Conclusion: Some instances of gum disease are likely caused or worsened by the suppression of the immune system.

Reasoning: People who avoid dealing with problems have higher rates of gum disease, and stress is known to negatively impact the immune system.

Analysis: The author is attempting to bridge a gap between a behavioral observation and a biological cause. To make this argument work, we must assume that the behavior of 'refusing to think about problems' actually results in more stress than addressing them directly. If ignoring problems were actually less stressful, the link to the immune system would vanish. Look for an answer that confirms avoiding problems is indeed a significant source of stress for these individuals.