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
Formula of hydroxyapatite crystal is 
Select and explain. 
A. Ca3 (Po4)2. CaCo3, B. 3Ca(Po4)2. Ca(OH)2, C. CaPo4. Ca(OH)2, D. None of the above
B: 3Ca(Po4)2. Ca(OH)2
Answer: B: 3Ca(Po4)2. Ca(OH)2 
Explanation: None