People who have spent a lot of time in contact with animals often develop animal-induced allergies, some of them quite serious. In a survey of current employees in major zoos, about 30 percent had animal-induced allergies. Based on this sample, experts conclude that among members of the general population who have spent a similarly large amount of time in close contact with animals, the percentage with animal-induced allergies is not 30 percent but substantially more. Which of the following, if true, provides the strongest grounds for the experts' conclusion? ['A zoo employee who develops a serious animal-induced allergy is very likely to switch to some other occupation.', 'The percentage of the general population whose level of exposure to animals matches that of a zoo employee is quite small.', 'Zoo employees seldom wear protective gear when they handle animals in their care.', 'A zoo employee is more likely than a person in the general population to keep one or more animal pets at home']