Aid workers have worried that residents of the Eastern Gobi Refugee Camp might be at risk for beriberi, a severe deficiency of Thiamine, a B vitamin. Thiamine is found in high concentrations in cereal grains, and many of the residents have grain free diets because of allergies. Doctors and nutritionists assigned to investigate the situation have disagreed, noting that the residents grow sustenance amounts of potatoes, kale, and cauliflower on the surrounding farm lands, and these foods provide substantial sources of Thiamine as well. Because the residents of this refugee camp do not have any allergies to any of these latter foods, and crops have been good because of favorable weather conditions, their risk of beriberi is much lower than originally thought.
In the argument given, the two portions in boldface play which of the following roles?