The correct answer is: C. Orange.
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 legume that is native to Africa and Asia. It is used in many cuisines as a flavoring agent. Tamarind contains tartaric acid, not citric acid.
Sour milk is milk that has been fermented by bacteria. It is a common ingredient in many cuisines. Sour milk contains lactic acid, not citric acid.
Tomatoes are a fruit that is native to South America. They are a popular ingredient in many cuisines. Tomatoes contain citric acid, but in much lower concentrations than citrus fruits.
Therefore, the correct answer is: C. Orange.