According to a study of more than 50,000 Norwegian smokers, smokers who reduced their nicotine intake from cigarettes, even by up to 50 percent, did not achieve significant health benefits. The mortality rate for those who cut back on cigarettes was not lower than that for heavier smokers; moreover, the rate of cardiovascular disease was similar across all subsets of smokers in the study. As a result, the sponsors of the study claim that reducing nicotine intake does not improve one's health.
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
OA is A. Why is C not an answer because it attacks the basic assumption that the inital level of nicotine intake - which means that we are not comparing apples to apples ? Please explain