In the linear regression model 1J1 = g + my; + .812; + U1. correlation between the regressoryz and the error term U1 may be caused by :3 a. measurement errors in ya. 0 b. omitted variables in u;. G c. the possibility that ya and y-l arejointiy determined by an "equilibrium" mechanism. (3 d. any ofthe above. 0 e. none of the above. In a simultaneous equations model (SEM), the number of structural equations is the same as O a. the number of endogenous variables in the SEM. O b. the number of exogenous variables in the SEM. O c. the number of exogenous and endogenous variables in the SEM. O d. none of the above