The Fixed Per-Unit Profit Contribution Coefficients of the Objective Function

The fixed per-unit profit contribution coefficients of the objective function in a linear programming problem imply the following economic assumptions except:

A) selling prices per unit of the products (outputs) are constant
B) constant returns to scale in the production process
C) buying prices per unit of the resources (inputs) are proportional to the amount purchased
D) both b and c
E) both a and c