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
[{'content': 'Pulp responds to all stimuli by pain because it has only \nSelect and explain. \nA. Free nerve endings, B. Krause end bulbs, C. Pacinian corpuscle, D. Ruffini corpuscle', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]