This does not affect the argument. Most business travel occurring between countries with contiguous borders doesn’t tell us about how similar those countries are culturally and climate-wise. We would have to make several assumptions for this to have any impact.

This does not affect the argument. It could be that people enjoy the experience but still feel the stresses described. Also, the argument claims travelling businesspeople are more likely to have insomnia—the author isn’t arguing that all of them do.

This strengthens the argument by addressing a potential alternative explanation for the phenomenon: that businesspeople who already have insomnia are more likely to travel than businesspeople who don’t have insomnia. This would mean the stress has nothing to do with it.

This does not affect the argument. (D) says people who already have insomnia may benefit from the stresses described. This is outside the scope of the causal mechanism described in the stimulus, which is that the stresses cause insomnia in the first place.

This does not affect the argument. We don’t know if these ailments include insomnia, which is what we’re concerned with. Also, the stimulus only discusses stress as the cause of insomnia for travelling businesspeople—other people can have insomnia for other reasons.