小明在欣赏茶艺表演的时候发现，表演者在改变茶水流出的方向时要不停的改变手拿茶壶的位置，这体现出[ ]

A、力的作用效果与力的大小有关  

B、力的作用效果与力的方向有关

C、力的作用效果与力的作用点有关

D、力的作用效果与以上三者都有关

Price discrimination is most accurately defined by which of the following Price discrimination is the practice of charging different consumers different prices for:（）

A. similar products that have identical per-unit production costs.

B. products that have identical price elasticities of demand.

C. the same product or service.