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 have greatest concentration of osteogenic cells: 
Select and explain. 
A. Marrow- cancellous graft., B. Marrow- cortical graft., C. Costochondral graft., D. Cortical graft
A: Marrow- cancellous graft.
Answer: A: Marrow- cancellous graft. 
Explanation: None