Which of the following most logically completes the argument?
When people engage in activities that help others ,their brain releases endorphins, the brain's natural opiates, which induce in people a feeling of well-being. It has been suggested that regular release of endorphins increases people's longevity. And a statistic on adults who regularly engage in volunteer work helping others shows that they live longer, on average, than adults who do not volunteer. However, that statistic would be what we would expect even if volunteering does not boost longevity, because____________.
A survey on adults who regularly engage in volunteer work helping others shows that they live longer, on average, than adults who do not volunteer.
Someone suggested that this result is due to the release of a chemical. But the author thinks not. The author says that women are more likely to volunteer and women are more likely to live longer. Therefore it is more likely to see a long-living woman as a volunteer, not volunteering work extends PEOPLE's lives.