Mr. Chen believes that there is not much relationship between smoking and health, because among the people he knows, several people with lung cancer are never smokers. If the following items are true, which one cannot refute Mr. Chen's view? ? ['The cause of cancer is a subject studied by many medical workers, and there is no definite conclusion yet.', 'Long-term smokers are more likely to develop lung cancer than smokers themselves.', 'Among the people Mr. Chen knows, the smokers are young guys, and the non-smokers are frail and elderly people.', 'Exclude people with lung cancer. Among the people Mr. Chen knows, smokers have significantly more people with respiratory diseases than never smokers.']