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': 'Source of Ca+2 in dentinal bridge is: \nSelect and explain. \nA. Blood, B. Ca(OH), C. saliva, D. ICF', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]