2. Heteroskedasticity and Serial Correlation a. (2 points) Consider a static model for time-series data Yt=Bo+B1xt + Ut, t = 1, 2, n , Write down the expressions of OLS estimators Bols, Bols. b. (4 points) Suppose yt is a dummy variable in (a). When are the standard OLS estimators unbiased? Are they efficient? Why or why not? If not, how would you obtain efficient estimators? c. (4 points) Suppose yt is takes continuous values in (a). Suppose ut aut-1 + t, Et ~i.i.d N(0,), |a| < 1. Is the standard OLS estimator efficient? Describe the Cochrane-Orcutt procedure.