substitution of rationing for exchange

例句：

1. 1.The company's decision to substitute a new product for the old one is causing some concern among customers.
   公司决定用新产品替换旧产品，这让一些顾客感到担忧。
2. 2. The scientist used a substitution to make the experiment more accurate.
   科学家使用一种替代方法使实验更准确。
3. 3. The teacher suggested that students use a substitution for their math homework instead of solving equations.
   老师建议学生用数学作业的替代方法而不是解方程来完成作业。