Final answer:
The conditions for returns to scale are matched with descriptions showing constant returns to scale in the middle flat portion of the long-run average cost curve, economies of scale when the average cost decreases with increased output, and the implication on firm sizes within a market.
Step-by-step explanation:
The question relates to economies of scale and how they impact the long-run average cost (LRAC) curve in different scales of production. The conditions to match to descriptions of returns to scale include constant returns to scale, which refers to a situation where increasing all inputs proportionally does not change the average cost of production. This typically occurs in the middle portion of the LRAC curve, where it flattens out, suggesting that economies of scale have been exhausted. When economies of scale are present, a firm is said to experience a decline in the average cost per unit as the scale of production increases, as is the case in industries where larger companies, like warehouse stores, can produce goods at a lower average cost per unit than smaller companies. Finally, if the LRAC curve has a flat-bottomed segment, firms in the market may come in various sizes since they experience constant returns to scale over that range, allowing them to operate efficiently at different output levels.