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: Dental
In fixed orthodontic treatment, how much force is needed for intrusion of four mandibular anterior teeth: 
Select and explain. 
A. 50 gm, B. 100gm, C. 150gm, D. 200gm
A: 50 gm
Answer: A: 50 gm 
Explanation: None