The correct answer is D. Lemon.
Citric acid is a weak organic acid found in citrus fruits. It is a white, odorless, crystalline solid that is soluble in water. Citric acid is used as a flavoring agent, preservative, and chelating agent.
Tamarind is a tropical fruit that is native to Africa and Asia. It has a sour taste due to the presence of citric acid.
Milk is a nutrient-rich liquid that is produced by mammals. It contains lactose, a type of sugar, and casein, a type of protein. Milk does not contain citric acid.
Apples are a type of fruit that is native to Europe and Asia. They have a sweet and tart taste due to the presence of citric acid and malic acid.
Lemons are a type of citrus fruit that is native to Asia. They have a sour taste due to the presence of citric acid.