People who do regular volunteer work tend to live longer, on average, than people who do not. It has been found that 'doing good.' a category that certainly includes volunteer work, releases endorphins, the brain's natural opiates, which induce in people a feeling of well-being. Clearly, there is a connection: Regular releases of endorphins must in some way help to extend people's lives.

Which of the following, it true most seriously undermine the force of the evidence given as support the hypothesis that endorphins promote longevity

(A) People who do regular volunteer work are only somewhat more likely than others to characterize the work they do for as a 'doing good.'

(B) Although extremely high levels of endorphins could be harmful to health, such levels are never reached as a result of the natural release of endorphins.

(C) There are many people who have done some volunteer work but who do not do such work regularly.

(D) People tend not to become involved in regular volunteer work unless they are healthy and energetic to begin with.

(E) Releases of endorphins are responsible for the sense of well-being experienced by many long-distance runners while running.

D