Medical researcher: As expected, records covering the last four years of ten major hospitals indicate that babies born prematurely were more likely to have low birth weights and to suffer from health problems than were babies not born prematurely. These records also indicate that mothers who had received adequate prenatal care were less likely to have low birth weight babies than were mothers who had received inadequate prenatal care. Adequate prenatal care, ttherefore, significantly decreases the risk of low birth weight babies. Which one of the following, if true, most weakens the medical researcher's argument? ['The hospital records indicate that low birth weight babies were routinely classified as having been born prematurely.', 'Mothers giving birth prematurely are routinely classified by hospitals as having received inadequate prenatal care when the record of that care is not available.', 'The hospital records indicate that many babies that are born with normal birth weights are born to mothers who had inadequate prenatal care.', 'Women who receive adequate prenatal care, are less likely to give birth prematurely than are women who do not receive adequate prenatal care.']