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': 'Which of these is not a type of healthy bone healing? \nSelect and explain. \nA. Contact healing, B. Gap healing, C. Healing with callus formation, D. Fibrous healing', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Primary healing - Contact and gap healing\nSecondary healing - healing with callus formation\nNon-union - fibrous / soft tissue ingrowth between segments or eburnated segment margins.', 'role': 'assistant'}]