Insurers and doctors are well aware that the incidence of lower-back injuries among office workers who spend long hours sitting is higher than that among people who regularly do physical work of a type known to place heavy stresses on the lower back. This shows that office equipment and furniture are not properly designed to promote workers' health. Which one of the following, if true, most undermines the reasoning above? ['Consistent physical exercise is one of the most effective ways to prevent or recover from lower-back injuries.', 'Most of the lower-back injuries that office workers suffer occur while they are on the job.', 'When they are at home, laborers and office workers tend to spend similar amounts of time sitting.', 'Insurance companies tend to dislike selling policies to companies whose workers often claim to have back pain.']