Researchers have found that children in large families -- particularly the younger siblings -- generally have fewer allergies than children in small families do. They hypothesize that exposure to germs during infancy makes people less likely to develop allergies. Which one of the following, if true, most supports the researchers' hypothesis? ['Children whose parents have allergies have an above-average likelihood of developing allergies themselves.', 'Children from small families who entered day care before age one were less likely to develop allergies than children from small families who entered day care later.', 'Children in small families generally eat more kinds of very allergenic foods than children in large families do.', 'Some allergies are life threatening, while many diseases caused by germs produce only temporary discomfort.']