The downward sloping part of the long-run average cost curve of a firm may be attributable to?

The downward sloping part of the long-run average cost curve of a firm may be attributable to "increasing returns to scale." This means that as a firm increases its scale of production, it experiences greater efficiency and cost savings, resulting in a lower average cost of production. In other words, as the firm expands its production capacity, it can take advantage of economies of scale, such as bulk purchasing of raw materials, specialized labor, and the use of more efficient technology, resulting in lower average costs. Therefore, the long-run average cost curve may slope downward due to increasing returns to scale.