Although marathons are 26. 2 miles (42. 2 kilometers) long and take even world-class marathoners over 2 hours to run, athletes who train by running 90 minutes a day fare better in marathons than do those who train by running 120 minutes or more a day. Each of the following, if true, contributes to an explanation of the difference in marathon performances described above EXCEPT: ['The longer the run, the more frequent is the occurrence of joint injuries that significantly interfere with overall training.', 'The longer the period of time that one runs daily, the easier it is to adjust to different race lengths.', 'Runners who train over 90 minutes per day grow bored with running and become less motivated.', 'The longer period of time that one runs daily, the greater the chances of suffering adverse health effects due to air pollution.']