Rats fed high doses of the artificial sweetener saccharin develop silicate crystals that are toxic to cells lining the bladder. When the cells regenerate, some are cancerous and form tumors. Unlike rats, mice fed high doses of saccharin do not get bladder cancer. Which one of the following, if true, does the most to resolve the apparent discrepancy in the information above? ['The silicate crystals are toxic only to the cells lining the bladder and not to other bladder cells.', 'Cells in the bladder regenerate more quickly in mice than they do in rats.', 'High doses of saccharin are much more likely to produce silicate crystals than lower doses are.', 'Urine proteins that react with saccharin to form silicate crystals are found in rats but not in mice.']