In a study of the impact of smoking on birth weight, researchers analyze birth weights (in grams) for babies born to 189 women who gave birth in 1989 at a hospital in massachusetts. in the group 74 were categorized as "smokers" and 115 as "nonsmokers." the difference in mean birth weights (nonsmokers minus smokers) is 281.7 grams with a margin of error of 205.2 grams with 95% confidence. which gives the best interpretation of what we can conclude about the impact of smoking on birth weight? a) we are 95% confident that on average, smoking causes lower birth weights of between 76.5 grams to 486.9 grams. b) there is a 95% chance that if a woman smokes during pregnancy her baby will weigh between 76.5 grams to 486.9 grams less than if she did not smoke. c) when smokers are compared to nonsmokers, we are 95% confident that the mean weight of babies of nonsmokers is between 76.5 grams to 486.9 grams more than the mean weight of babies of smokers. d) this study does not suggest that there is a difference in mean birth weights when we compare smokers to nonsmokers.