A company paid $200,000 ten years ago for a specialized machine that has no salvage value and is being depreciated at the rate of $10,000 per year. The company is considering using the machine in a new project that will have incremental revenues of $28,000 per year and annual cash expenses of $20,000. In analyzing the new project, the $10,000 depreciation on the machine is an example of a(n):
a. Incremental cost.
b. Opportunity cost.
c. Variable cost.
d. Sunk cost.
e. Out-of-pocket cost.