A 51-year-old man presents to his physician for evaluation of his risk for heart disease. The patient is very concerned about his chance for a heart attack because his father died at age 53 from a massive infarction. The patient reports that he eats well, exercises regularly, and has been told by his workplace screening program that he has "normal" cholesterol levels. On questioning, he reports that he had previously smoked one pack per day for about 20 years but quit 2 years ago. How many years must this patient have stopped smoking before his tobacco use no longer counts as a risk factor? A. 1 year B. 5 years C. 10 years D. 15 years E. 20 years D.15 years ( the risk is decreased by 50% within 1 year of quitting,but decreased to that of people who never smoked 15 years after quitting) in 5yrs the risk of lung ca is reduced to 50% and and same as one who has never smoked in 10yrs.