A study found that each additional year of work amounted to a 6-week delay in the development of Alzheimer's disease. Therefore, delaying retirement may help stave off Alzheimer's. Which of the following statements, if true, would most seriously weaken the above argument?

O Individuals who retire later are less likely to eigage in other activities to remain mentally sharp.
O Adults who retire early often do so because of chronic health conditions, which contribute to the development of Alzheimers.
O The mental stimulation of work may help keep brain cells connected, which delays the development of Alzheimer's.
O All patients in the study were men, rendering the results invalid for women.
O Neither the quality of education nor the type of work impacts the age of Alzheimer's onset.