Final answer:
Efficient size of operations is most closely related to the concept of economies of scale, where as production scale increases, the cost per unit decreases due to cost advantages gained by the size of the operations.
Step-by-step explanation:
The question 'Efficient size of operations is related to which of the following concepts?' pertains to the business concept of economies of scale. Economies of scale are the cost advantages industries obtain due to size. The idea is that as a business or operation grows and the quantity of output increases, the cost per individual unit decreases.
This is observed in large warehouse stores like Costco or Walmart, which can sell products at a lower cost due to their large-scale operations compared to smaller retail outlets. Another example is a larger factory which can produce goods at a lower average cost than a smaller factory, owing to factors like more efficient use of production technology and a better allocation of fixed costs over more units of output.
In conclusion, the efficient size of operations is most closely related to the concept of economies of scale, making the correct answer D.