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
In gate control theory of pain, pain is modulated by: 
Select and explain. 
A. A-delta fibres., B. Substantia gelatinosa., C. B fibres., D. C fibres.
B: Substantia gelatinosa.
Answer: B: Substantia gelatinosa. 
Explanation: None