Employees of companies that offer corporate fitness programs consistently take fewer sick-days than do employees of companies that do not offer fitness programs. Thus, corporate fitness programs are shown to have a positive effect on the health of a company's workforce.
Which of the following, if true, most seriously weakens the argument above?
A. Other benefits offered by companies that do not offer corporate fitness programs surpass the benefits offered by companies that do offer such programs.
B. Companies that offer corporate fitness programs attract employees who are more health conscious than the employees of companies that do not offer such programs.
C. The health benefits of a corporate fitness program depend upon the particular makeup of the program.
D. Employees who participate in corporate fitness programs are not measurably less healthy than people who exercise on their own.
E. People who participate in fitness programs not offered by their employees are generally healthier than people who participate in corporate fitness programs.