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: Pharmacology
[{'content': 'Analgesic that itself can cause headache as a side effect is : \nSelect and explain. \nA. Indomethacin, B. Mefenamic acid, C. Piroxicam, D. Aspirin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]