The correct answer is B. Lactic acid.
Lactic acid is a type of organic acid that is produced by the fermentation of sugars. It is found in sour milk, yogurt, and cheese. It is also produced by the body during exercise.
Citric acid is a type of organic acid that is found in citrus fruits, such as lemons and limes. It is also used as a food additive and preservative.
Tartaric acid is a type of organic acid that is found in grapes and other fruits. It is also used as a food additive and preservative.
Acetic acid is a type of organic acid that is found in vinegar. It is also used as a food additive and preservative.
Lactic acid is the main acid found in curd. It is produced by the fermentation of lactose, the sugar found in milk, by bacteria. The lactic acid gives curd its sour taste and also helps to preserve it.