\begin{tabular}{l}\hline 9\( ) \) Ting owns a diamond shop. Last year her average cost of selling a \\ diamond was \( \$ 990 \). If she expands the size of her store this year and \\ sees her average cost decrease to \( \$ 850 \), her long-run average total \\ cost curve should be _- \\ OA) downward sloping. \\ OB) upward sloping. \\ OC) U-shaped. \\ OD) horizontal. \end{tabular}

If Ting's average cost of selling diamonds has decreased as she expands her store, it suggests that she is experiencing economies of scale. This means that as her production increases, her average costs decrease, leading to a more efficient operation. Hence, the long-run average total cost curve should be **downward sloping** (Option A). Additionally, in the long run, businesses often strive for efficiency. If Ting's average costs continue to decrease with increased sales, she can invest in higher-quality inventory or enhanced customer experiences. Thus, her strategic focus should be on achieving sustainable growth to maintain this lower cost structure while maximizing her profit margins.