Karen P is using an old machine that only has three years of useful life remaining to make most of its products. The company has been purchasing part #1967 that is used to make the "Danger Will Robinson" robot from LIS company. Now, Karen Pis contemplating making part #1967 on the old machine. In this decision (whether to make or to buy part #1967), the $20,000 annual depreciation (for each of the three remaining years) on the old machine is an) Select one: a. Relevant Cost b. Opportunity Cost c. Sunk Cost d. Incremental Cost