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 type of Distraction osteogenesis does not involve transport disc? 
Select and explain. 
A. Unifocal, B. Bifocal, C. Trifocal, D. Alveolar Distraction
A: Unifocal
Answer: A: Unifocal 
Explanation: None