Researchers have noticed that people whose blood shows abnormally low levels of calcium usually have laryngeal polyps, which can permanently damage vocal cords and result in partial or even total loss of voice. In order to reduce the risk of polyps, the researchers recommend a diet high in calcium-rich foods such as dairy and green, leafy vegetables. Which of the following, if true, most strongly suggests that following the researchers' recommendation would NOT be effective? ['Fresh vegetables are not always available in all seasons.', 'Low levels of calcium can sometimes be remedied with vitamin pills.', 'Laryngeal polyps sometimes disappear without treatment.', 'Laryngeal polyps cause a change in body chemistry that blocks the absorption of calcium.']