The correct answer is option 2: milk. Lactose is a type of sugar that is naturally present in milk and milk products. It is a disaccharide composed of glucose and galactose molecules. Lactose is unique to mammalian milk and is produced by the mammary glands of mammals, including humans. It serves as a source of energy for newborns and infants. Lactose is not present in grapes (option 1), lime (option 3), or vinegar (option 4). Grapes contain fructose, lime contains citric acid, and vinegar is produced from the fermentation of ethanol by acetic acid bacteria. Therefore, the correct option is option 2: milk.