单选题 Based on the concept of diminishing returns, as the quantity of output increases, the short-run marginal costs of production eventually:

A. rise at a decreasing rate.
B. rise at an increasing rate.
C. fall at an increasing rate.

【正确答案】 B

【答案解析】The law of diminishing returns states that as more variable resources are a production process combined with a fixed input, output will eventually increase at a decreasing rate. In the short run, as the quantity produced rises, costs rise at an increasing rate.