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
[{'content': 'Gate control theory of pain is due to \nSelect and explain. \nA. Substantial gelatinosa, B. A delta fibres, C. C-fibres, D. Free nerve endings', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]