Choice "D" is correct. The original cost of the old machine is a sunk cost that will not change regardless of the decision that is made. Sunk costs are not relevant and would not be considered by ABC as part of their decision to keep or replace the current machine.
Choice "c" is incorrect. The estimated salvage value of the old machine is relevant to the decision to keep or replace the machine. The salvage value will be realized if the machine is replaced but not realized if the old machine is not replaced.
Choice "b" is incorrect. The estimated useful life of the new machine is relevant to the decision to keep or replace the old machine. The useful life of the new machine will impact the comparative productive capacity of the company and would be considered in the decision.
Choice "a" is incorrect. The lower maintenance cost of the new machine is relevant to the decision to keep or replace the old machine. The maintenance cost of the new machine will impact the comparative operating costs of the company and would be considered in the decision.