边际效用论
参考答案：
价值决定于商品的最不重要部分的效用理论。
We have two spare rooms downstairs, ______ has been used for more than two months.
A．neither of them
B．none of which
C．none of them
D．neither of which
进货率低于80%说明（）。
A、进货量小
B、进货量适中
C、进货量不能满足销售
D、库存过量
