This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'The most common pre-eruptive staining is: \nSelect and explain. \nA. Amelogenesis imperfecta., B. Dentinogenesis imperfecta., C. Endemic fluorosis., D. Pulp necrosis.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Intrinsic colors are determined\xa0by optical properties of enamel and dentin and\xa0their interaction with light. If incorporated into\xa0the dentin, they become visible because of the\xa0translucency of the enamel. They can be related\xa0to periods of tooth development, as in amelogenesis imperfecta\xa0 or dentinogenesis\xa0imperfecta or they may be acquired\xa0after completion of tooth development, as in pulp\xa0necrosis. The most common pre-eruptive staining\xa0is endemic fluorosis caused by excessive\xa0fluoride ingestion during tooth development.', 'role': 'assistant'}]