The Additivity Feature of Linear Programming (LP) Models Assumes All

The additivity feature of linear programming (LP) models assumes all of the following except that:

A) The contribution of decision variables to the objective function is proportional.
B) The contribution of each decision variable can be added to obtain the overall usage of a given constraint.
C) The contribution of each decision variable can be added to obtain the overall value of the objective function.
D) All of the above are features of proportionality in LP.