Passage Summary: Obesity is a massive health crisis, but many doctors say they don't know how to help. Therefore, we need to give them more training.

Conclusion: Medical professionals require additional training specifically focused on treating obesity.

Reasoning: Obesity is set to become the primary cause of preventable illness, yet nearly half of surveyed doctors admit they lack the expertise to advise patients on the matter.

Analysis: The argument identifies a gap between a significant health need and the current skills of doctors. To bridge this gap, we need a principle that mandates training when such a discrepancy exists. Look for an answer that states if a health issue is a major public concern, doctors have an obligation to be competent in treating it. It's a straightforward 'problem-solution' structure that needs a rule to make the solution mandatory.