Final answer:
A best practice refers to methods consistently proven to yield superior results than others, closely related to the concepts of economies of scale and core competency within businesses. Option D is correct.
Step-by-step explanation:
A "best practice" is not merely about finding the lowest-cost procedure or achieving a specific defect rate. It is about methodologies that have been consistently proven to yield superior results. Answer D) is a method of performing an activity that has been shown consistently deliver superior results compared to other methods, aligns with this definition.
In businesses, this concept parallels the idea of economies of scale where larger production volumes lead to lower per-unit costs. Additionally, core competency, the particular area where a business excels the most, often contributes to a firm's competitive advantage and can be considered a best practice in its right.