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: Forensic Medicine
[{'content': 'FG, FFG, FFFG ... used to describe: \nSelect and explain. \nA. Primer, B. Caridge, C. Black gunpowder, D. Base of firearms', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. Black gunpowder', 'role': 'assistant'}]