substitution of variable

例句：

1. 1.The new model car is a perfect substitute for the old one.
   新款汽车是旧款汽车的完美替代品。
2. 2. The scientist used different materials to substitute for the lost parts.
   科学家用不同的材料来替换丢失的部分。
3. 3.The teacher asked students to substitute their homework with their own work.
   老师要求学生用自己的作业代替家庭作业。