若产量增加，而生产费用不变，则单位成本指数
A.减少
B.不变
C.增加
D.无法预期变化
正确答案是A
Choose the closest paraphrased version after the following sentence or the italicized part.
Sometimes I think how grateful I would be today if I had learned more back then about what really matters.（ ）
将题43图所示的E-R图转换成对应的关系模型,并注明主码。
