老师在课堂上做了几次换人。

The teacher made several ___substitutions during the class.

在烘焙时，苹果酱可以作为鸡蛋的替代品。

In baking, applesauce can be a good ___substitute for eggs.

在正式写作中，我们经常用同义词作为替换以避免重复。

In formal writing, we often use synonyms as ___substitutions to avoid repetition.