Final answer:
Companies focused on improving quality hire Six Sigma Black Belts to work on identifying the root cause of problems and implementing solutions. Hiring Black Belts to keep defects from occurring to begin with results in prevention costs.
Step-by-step explanation:
When companies hire Six Sigma Black Belts to work on improving quality by identifying the root cause of problems and implementing solutions, they are focusing on prevention of defects. Hiring Black Belts helps to keep defects from occurring in the first place, which is a form of prevention cost.
Prevention costs are incurred to prevent defects from happening, and they include activities such as training, quality planning, process documentation, and implementing quality control measures. By investing in prevention, companies aim to reduce the occurrence of defects and ensure higher quality products or services.
Therefore, the answer is D. prevention.