In a recent study of dust-mite allergy sufferers, one group slept on mite-proof bedding, while a control group slept on bedding that was not mite-proof. The group using mite-proof bedding had a 69 percent reduction in the dust-mite allergen in their mattresses, whereas there was no significant reduction in the control group. However, even though bedding is the main source of exposure to dust mites, no symptom reduction was reported in either group. Which one of the following, if true, most helps to resolve the apparent conflict in the statements above? ['The medical community does not fully understand how dust-mite allergens cause allergy.', "Dust-mite allergens in bedding tend to irritate many allergy sufferers' nasal passages more than do the same allergens in other locations, such as carpets.", 'When people report their own allergy symptoms, they tend to exaggerate the severity of those symptoms.', 'For dust-mite allergy sufferers to get relief from their allergies, dust-mite allergens must be reduced by 90 to 95 percent.']