Health association: In certain studies, most volunteers who used to eat meat have permanently excluded meat from their diets and now eat only vegetables and fruits. These volunteers suffered no ill effects and many even prefer the new regimen. So people who eat meat can change their diets to meatless ones and not suffer as a result. Critic: Participants in these studies were all favorably disposed to the substitution before they started, and even so, many of them failed to make a complete transition to a vegetarian diet. The critic's response would most seriously call into question which one of the following conclusions, if that conclusion were drawn on the basis of the evidence given by the health association? ['Participants in the study who failed to make the transition to a vegetarian diet do not regret the attempt.', 'The diets of most people who eat meat would be improved if those people ate only vegetables and fruits instead.', 'The number of people who have adopted a strictly vegetarian diet has increased in the last few years.', 'Most people, if told by their physicians to exclude meat from their diets and eat only vegetables and fruits, would succeed in doing so.']