Final answer:
Adding buttermilk to chilled milk is likely to make the milk both more sour and more acidic due to the presence of lactic acid bacteria in buttermilk. Depending on the freshness and acidity of the milk and buttermilk, the mixture could also potentially curdle.
Step-by-step explanation:
If you add buttermilk to chilled milk, the mixture will most likely become both more sour and more acidic (Options B and D). This is because buttermilk contains bacteria known as lactic acid bacteria, which metabolize the sugars in the milk and create lactic acid as a byproduct. This process is what gives buttermilk its distinctive tart flavor. The acidification could also lead the mixture to curdle (Option A), especially if the milk was close to its expiration date or if the buttermilk had a particularly high level of acidity. However, if the milk was fresh and well-chilled, and the buttermilk did not excessively acidic, curdling might not occur and the milk might simply become tangier and more flavorful without changing its texture significantly (not fully agreeing with Option C).
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