如果一个企业降低其产品价格后，发现收入增加，这意味着( )。

A．商品需求缺乏价格弹性
B．商品需求富有价格弹性
C．商品需求具有单位价格弹性
D．商品需求曲线向下倾斜

What I want to say is that our class won't be able to finish the work unless we________each other.[ ]

A. team up with  

B. come up with    

C. put up with      

D. catch up with