In the presence of serial correlation a. estimated OLS values are not BLUE b. estimated variance does not differ from the case of no serial correlation c. estimated standard errors remain valid d. estimated test statistics remain valid Consider the regression model below. yi=0+1xi+ui If the first four Gauss-Markov assumptions hold true, and the error term contains heteroskedasticity, then a. Var(uixi)= b. Var(uixi)=0 c. Var(uixi)=1 d. Var(uixi)=i2 ln(wage)=1.439+0.0834edu+0.0512exper+0.1932male Where: wageeduexpermaleishourlywageisyearsofeducationisyearsofrelevantexperienceindicatesthattheemployeeismale the researcher? Oa.ln(wage)=0+1edu+2exper+3male+uOb.ln(wage)=0+1exper+2male+uOc.ln(wage)=0+1(expermale)+ud.ln(wage)=0+1edu+2exper+3male+4(expermale)+u