单选题 Which of the following most accurately describes the shapes of the average variable cost (AVC) and average total cost (ATC) curves?

A. The AVC and ATC curves are both U-shaped.
B. The AVC and ATC curves both decrease initially, and then flatten.
C. The AVC curve is U-shaped whereas the ATC curve declines initially then flattens.

【正确答案】 A

【答案解析】The AVC curve is U-shaped, declining at first due to efficiency, but eventually increasing due to diminishing returns. The AFC curve decreases as output increases, and eventually flattens out. The ATC is U-shape because it is the sum of the decreasing-to-flat AFC curve plus the U-shaped AVC + curve. ATC = AFC + AVC.