John: For 40 years, fluoride has been added to public drinking water. According to a study, fluoridated public drinking water when given to laboratory rats causes bone cancer. Ninety percent of all the male rats in the test sample were affected, but the female rats were unaffected. Even though I am healthy now, I should nevertheless stop drinking fluoridated water; only then will I be sure not to develop bone cancer. Which one of the following is the strongest criticism of John's reasoning? ['John does not consider whether fluoridated water causes other diseases.', 'John does not consider whether there were any brief periods during the 40 years in which fluoride was not added to the water.', 'John does not consider the possibility of other causes of bone cancer.', 'John does not focus on the positive effects that fluoridated water has on people']