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: Radiology
[{'content': 'The minimum amount of tooth demineralization required for radiographic detection of dental caries is \nSelect and explain. \nA. 20%, B. 40%, C. 60%, D. 80%', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Lesions\xa0confined\xa0to\xa0enamel\xa0may\xa0not\xa0be evident\xa0until\xa0approximately\xa030%\xa0to\xa040% demineralization\xa0has occurred.\xa0For\xa0this\xa0reason,\xa0the\xa0actual\xa0depth\xa0of\xa0penetration\xa0of\xa0a carious lesion is often deeper than seen in the image.\n\xa0\nOral radiology by White & Pharaoh 7th ed. Page no 288', 'role': 'assistant'}]