The correct answer is D. regulate their own processes . In Six Sigma and lean thinking, a defect can only be considered worker-controllable when the worker has direct influence over the conditions that create or prevent that defect. If operators are not allowed to adjust, regulate, or control the process they are running, then they do not truly own the source of variation and cannot reasonably be held accountable for the resulting defects. CSSBB material on standard work emphasizes that workers, machines, and materials must be combined in a controlled work environment, and it includes concepts such as worker ideas valued , defective prevention , and autonomous systems installed as part of effective standard work.

This aligns with the broader Six Sigma principle that defects should be assigned only where control exists. Job rotation, cross-functional participation, and customer complaint review may improve awareness and engagement, but they do not give the worker direct process control. To classify a defect as worker-controllable, the worker must be able to monitor and act on the process conditions that drive output. Therefore, the best answer is D .