These days, drug companies and health professionals alike are focusing their attention on cholesterol in the blood. The more cholesterol we have in our blood, the higher the risk that we shall die of a heart attack. The issue is pertinent since heart disease kills more North Americans every year than any other single cause. At least three factors -- smoking, drinking, and exercise -- can each influence levels of cholesterol in the blood. Which one of the following can be properly concluded from the passage? ['Smoking in moderation can entail as great a risk of fatal heart disease as does heavy smoking.', "The only way that smoking increases one's risk of fatal heart disease is by influencing the levels of cholesterol in the blood.", 'The risk of fatal heart disease can be altered by certain changes in lifestyle.', 'A high-cholesterol diet is the principal cause of death in North America.']