Passage Summary: Business people who fly abroad a lot can't sleep well, and since they deal with weird weather and new cultures, the author blames those stresses for the sleeplessness.

Conclusion: The specific stresses associated with international travel are the likely cause of increased insomnia among businesspeople.

Reasoning: There is a correlation between international business travel and chronic insomnia, and these travelers face unique stressors like climate changes and routine disruptions that non-travelers do not.

Analysis: To strengthen this causal argument, we need to shore up the link between travel stress and insomnia while fending off alternative explanations. The argument currently relies on a simple correlation; it assumes that the travel causes the insomnia rather than the other way around. Look for an answer that rules out 'reverse causality'—perhaps by showing that these individuals didn't have insomnia before they started traveling. In the world of business travel, it's also possible that the coffee or the late-night meetings are the culprits, so an answer that isolates the 'stress' factor would be a major win.