Consider a typical product mix model where the decision variables are the quantities of the various products to produce and the objective is to maximize the sum of the profits from the various products. Suppose that one term in this sum equals 120 when 5 units of the corresponding product are produced, and it equals 140 when 10 units of that product are produced. Which of the following is true? a. The model isn't linear because the proportionality condition isn't satisfied.
b. The model isn't linear because neither the proportionality nor the additivity condition is satisfied.
c. The information given doesn't rule out the possibility that the model is linear.
d. The model isn't linear because the additivity condition isn't satisfied.