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: Physiology
[{'content': 'Sensory receptors for pain are \nSelect and explain. \nA. Pacinian corpuscles, B. End organs of Ruffini, C. End bulbs of Krause, D. Free nerve endings', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]