In a structural equation of the simultaneous equations model (SEM) for the housing demand and supply in Sydney, the error term is generally correlated with the endogenous regressor. In this SEM context, the most important reason for the correlation is a. that the regressor may carry measurement error. b. that the regressar may be correlated with an omitted variable. c. that the dependent variable may carry measurement error. d. that the dependent variable may be correlated with an omitted variable