law of reciprocal demand

例句：

1. 1. The two companies havea reciprocal agreement on theirproducts.
   这两家公司拥有关于产品的互惠协议。
2. 2.The teacher and the student are both reciprocal friends.
   老师和学生都是彼此的朋友。
3. 3. The law of reciprocal demand states that if one party iswilling to give more than they receive,then the other party will be willing togive less.
   互惠需求法则指出，如果一方愿意给予的比得到的多，那么另一方就会愿意给予的少。