Which of the following, if true, most seriously jeopardizes the findings of the study described above? A. The majority of study participants minimized their nicotine withdrawal symptoms through the use of skin patches and chewing gum that provide nicotine to the body. B. Many of the study's participants periodically dined in restaurants in which smoking was permitted. C. The study's participants started smoking at different ages and had varied initial nicotine intake. D. Quitting smoking entirely results in a marked reduction in the ill effects of smoking. E. Men and women who smoked pipes and cigars were excluded from the study.