An article in the June 10, 2002, issue of the Archives of Internal Medicine reported on a study of the effectiveness of a nicotine lozenge for helping smokers to quit smoking. Smokers who participated in the study were randomly assigned to receive either the nicotine lozenge being tested or a placebo (no active ingredient) lozenge. Several variables were recorded on each subject at the beginning of the study, such as weight, gender, number of cigarettes smoked per day, and whether or not the person had made previous attempts to quit smoking. At the end of the study, the primary variable recorded was whether or not the subject had successfully refrained from smoking. a. Identify the observational units in this study. b. Identify the categorical variables mentioned in the preceding paragraph. c. Identify the quantitative variables mentioned in the preceding paragraph.