Classify the following as slow and fast changes.
Curdling of milk by adding lemon juice

Explanation

**Step-by-Step Solution:**

1. **Understanding the Process**: When lemon juice is added to milk, a chemical reaction occurs. The acid in lemon juice causes the proteins in the milk to coagulate, leading to the formation of curds.

2. **Identifying the Time Frame**: The curdling process happens relatively quickly, typically within a few minutes after adding the lemon juice.

3. **Classifying the Change**: Since the curdling of milk occurs in a short amount of time (minutes), it is classified as a fast change.

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