15. Perfect Plumbing Corporation currently manufactures a valve for use in water pumps that it produces for sale. The company is considering purchasing the valves from an outside supplier rather than manufacturing them. Which of the following costs is not relevant to the decision? A. The cost of direct material required to make the valve. B. The price charged by the outside supplier for an identical valve. C. The cost of the machinery owned by Perfect Plumbing used exclusively to manufacture this valve. D. The salvage value of the machinery owned by Perfect Plumbing used exclusively to manufacture this valve