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: Surgery
[{'content': 'Compression osteosynthesis heals fracture mandible by: \nSelect and explain. \nA. Primary union with out callus formation, B. Secondary union with out callus formation, C. Compression union, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]