在烘焙时，我们可以用苹果酱替代黄油来做出更健康的选择。

In baking, we can make a healthy ___substitution by replacing butter with applesauce.

当主力球员受伤时，教练决定用替补球员作为替代。

When the star player got injured, the coach decided to use a ___substitution on the field.

通过将y替换为2，我们可以简化这个方程式。

We can simplify the equation by ___substituting y with 2.