Which of the Following Statements Is Not Correct

Which of the following statements is not correct?

A) Depreciation expense is irrelevant with respect to an outsourcing decision.
B) Unavoidable fixed costs are irrelevant with respect to a decision to drop a product line.
C) Variable production costs are relevant with respect to a special sales order decision.
D) Avoidable fixed costs are irrelevant with respect to a make or buy decision.