The arguments has a cause-effect relationship:
Start fitness program in a company --> decrease in absentee rate in the company
(A) Employees who exercise during working hours occasionally fall asleep for short periods of time after they exercise.
No Impact, this option doesn't show the impact of fitness program on the absentee rate.
(B) Employees who are frequently absent are the least likely to cooperate with or join a cooperate fitness program.
Weakens, if the probability of frequent absentees joining the program is very low then it reduces the belief that company's plan will work.
(C) Employees who exercise only once a week in their company's fitness program usually also exercise after work.
No Impact, this option doesn't have a clear impact on the conclusion, it just talks about a particular subset of employees who exercise only once a week.
(D) Employees who exercise in their company's fitness program use their working time no more productively than those who do not exercise.
No Impact, this option shows the impact on productivity but doesn't show the impact of fitness program on the absentee rate.
(E) Employees who exercise during working hour take slightly longer lunch breaks than employees who do not exercise.
No Impact, this option shows the impact on lunch breaks but doesn't show the impact of fitness program on the absentee rate.