Ina simultaneous equations model (SEM), a reduced-form equation is a regression model where the dependent variable is an endogenous variable in the SEM and the regressors generally include a. all the endogenous variables in the SEM. b. only one of the endogenous variables (other than the dependent variable) in the SEM. c. all the exogenous variables in the SEM. d. only one of the exogenous variables in the SEM