Physiological research has uncovered disturbing evidence linking a number of structural disorders to jogging. Among the ailments seemingly connected with this now-popular sport are spinal disk displacements, stress fractures of the feet and ankles, knee and hip joint deterioration, and tendonitis. Furthermore, these injuries do not occur exclusively among beginning runners -- veteran joggers suffer an equal percentage of injuries. What the accumulating data suggest is that the human anatomy is not able to withstand the stresses of jogging. Which one of the following is an assumption of the argument? ['Some sports are safer for the human body than jogging.', 'Jogging causes more serious disorders than other sports.', 'The link between jogging and certain structural disorders appears to be a causal one.', "The jogger's level of experience is a factor determining the likelihood of a jogging injury."]