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 the following is the first target of distraction force? 
Select and explain. 
A. Osteoclasts, B. Osteoblasts, C. Mononuclear cells, D. Endothelial cells
D: Endothelial cells
Answer: D: Endothelial cells 
Explanation: None