使用“冲沙包”方法过浅区的条件是（）.
A、沙包体积不大
B、沙包是新淤积的
C、船舶船体强度较好
D、以上都对
参考答案：D
Which of the following conditions is most likely to exist for a typical production process when average product is at its maximum（）
A. Marginal product is increasing.
B. Marginal product is at a minimum.
C. Average variable cost is at a minimum.
