Choice "D" is correct. Rework cost is a cost of quality caused by internal failure. Cost of quality includes conformance costs (the costs of prevention and appraisal activities before product shipment) and nonconformance costs (the costs of internal and external failures that require either return of the product or rework of the product).
Choice "b" is incorrect. Rework caused by a customer error is not a cost of quality.
Choices "c" and "a" are incorrect. Rework caused by internal failure is a cost of quality, but rework caused by a customer is not a cost of quality.
