Many companies have found out through internal surveys

Many companies have found out through internal surveys that employee productivity is affected due to stress. Employees experiencing some sort of stress can be classified into one of the following 2 groups: those who suffered from work-related stress and those who suffered from stress in their personal lives. One leading multinational, which had conducted such a survey has developed a joint 5 day workshop on Stress Management for all its employees, designed to enable them to handle stress through an easy four-step method. The management believes that the workshop will help employees to de-stress and thus improve their productivity.

Which of the following, if true, casts the most serious doubt on the efficacy of the management's strategy to improve the productivity of the stressed-out employees?

A. Employee productivity, like all other performance variables, has an upper limit; it cannot increase beyond a certain limit.
B. It has been scientifically proven that stress leads to a decrease in not only productivity but also the quality of work
C. Many employees do not report personal stress and hence may not be included in the workshop in the first place.
D. Stress is only one of the factors that affect productivity, studies have suggested that office space comforts and relationships between employees are more important factors.
E. Personal and work-related stress are totally different from each other, while the latter can be treated in a workshop, the former needs personal psychiatric counselling.

Source - IMS GMAT Tests