What Are Reduced Form Equations in a System of Equations

Multiple Choice

What are reduced form equations in a system of equations?

A) the structural equations rewritten with endogenous variables as a function of exogenous variables
B) the structural equations without the endogenous regressors
C) the exogenous variables reworked as a function of the other exogenous variables
D) the equations remaining when the parameters of structural equations are reduced to generate additional degrees of freedom