Advice columnist: Several scientific studies have shown that, when participating in competitive sports, those people who have recently been experiencing major stress in their lives are several times more likely to suffer serious injuries than are other participants in competitive sports. Since risking serious injury is unwise, no sports activity should be used as a method for coping with stress. Which one of the following principles, if valid, most helps to justify the reasoning in the advice columnist's argument? ['When people have been under considerable stress, they should engage in competitive activities in order to relieve the stress.', 'A method for coping with stress should be used only if it has been subjected to scientific study.', 'People with a history of sports injuries should not engage in sports activities if they have recently been under stress.', 'If people recently under stress should avoid a subset of activities of a certain type, they should avoid all activities of that type.']