A certain gene can be stimulated by chemicals in cigarette smoke, causing lung cells to metabolize the chemicals in a way that makes the cells cancerous. Yet smokers in whom this gene is not stimulated have as high a risk of developing lung cancer from smoking as other smokers do. If the statements above are true, it can be concluded on the basis of them that ['the gene is more likely to be stimulated by chemicals in cigarette smoke than by other chemicals', 'stimulation of the gene by chemicals in cigarette smoke is not the only factor affecting the risk for smokers of developing lung cancer', 'nonsmokers have as high a risk of developing lung cancer as do smokers in whom the gene has not been stimulated', 'smokers are less likely to develop lung cancer if they do not have the gene']