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: Social & Preventive Medicine
[{'content': 'RDA of calcium for a normal adult male is: \nSelect and explain. \nA. 100 mg, B. 400 mg, C. 800 mg, D. 1200 mg', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 400 mg', 'role': 'assistant'}]