Final answer:
When we model the cost function as linear, we assume that the cost per refrigerator remains constant option C.
Step-by-step explanation:
When we model the cost function as linear, we are assuming that the cost per refrigerator remains constant. This means that for every additional refrigerator produced, the cost will remain the same. This assumption allows us to create a linear relationship between the number of refrigerators and the total cost.
For example, if producing 10 refrigerators costs $1000, then producing 20 refrigerators would cost $2000, assuming a constant cost per refrigerator.