Hayes Company currently buys a part for their final product at a cost of $150 per unit. They are considering making the part as they have enough extra capacity in their plant to make the part without leaving the relevant range. Direct Materials costs will be $40 per unit, Direct Labor $50 per unit and variable overhead is applied using machine hours. It requires 2 hours at $15 per machine hour. Fixed overhead is also applied at a rate of $10 per machine hours and requires 2 hours. How would you describe fixed overhead in this case?

A. A relevant cost

B. An avoidable cost

C. An unavoidable cost

D. A period cost