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
RDA of calcium for a normal adult male is: 
Select and explain. 
A. 100 mg, B. 400 mg, C. 800 mg, D. 1200 mg
B: 400 mg
Answer: B: 400 mg 
Explanation: 400 mg