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: Pathology
[{'content': 'Internal resorption is characterised by \nSelect and explain. \nA. Pain on percussion, B. Slow dull continuous pain, C. No characteristic feature, symptom free, D. Increased pulpal pain when lying down', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]