E7.1 Use the Birthweight Smoking data set introduced in Empirical Exercise E5.3 to answer the following questions. To begin, run three regressions: (1) Birthweight on Smoker (2) Birthweight on Smoker, Alcohol, and Nprevist (3) Birthweight on Smoker, Alcohol, Nprevist, and Unmarried a. What is the value of the estimated effect of smoking on birth weight in each of the regressions? c. Does the coefficient on Smoker in regression (1) suffer from omitted variable bias? Explain. d. Does the coefficient on Smoker in regression (2) suffer from omitted variable bias? Explain.