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
Which of these is not a type of healthy bone healing? 
Select and explain. 
A. Contact healing, B. Gap healing, C. Healing with callus formation, D. Fibrous healing
D: Fibrous healing
Answer: D: Fibrous healing 
Explanation: Primary healing - Contact and gap healing
Secondary healing - healing with callus formation
Non-union - fibrous / soft tissue ingrowth between segments or eburnated segment margins.