A6. In a small study in a hospital in Nashville, researchers compared the birth weights of babies born to mothers who used marijuana during pregnancy with the birth weights of infants born to mothers who did not. The difference in the sample averages (nonuser mothers vs. user mothers) was 280 grams. (a) Is this study an observational study or a randomized experiment? Explain your answer.s (b) Who are the subjects in this case? (c) What is the explanatory variable in this case? What is the response variable? Identify each as qualitative or quantitative. (d) What are the treatments in this case?