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': 'Double base smokeless gun powder contains the following elements: \nSelect and explain. \nA. Nitrocellulose and nitroglycerine, B. Potassium nitrate and nitroglycerine, C. Potassium nitrate and lead, D. Nitrocellulose', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Smokeless powders: They produce much less flame and smoke and are more completely burnt than black powder. Three types; Gun cotton: Consists of nitrocellulose Double-base powder: Consists of nitroglycerine and nitrocellulose Triple base powder: Consists of nitrocellulose, nitroglycerine and nitroguanidine Semi-smokeless powder is a mixture of 80% of black and 20% of the smokeless type. Ref: The Essentials of Forensic Medicine and Toxicology by K S Reddy, 27th edition, Page 188.', 'role': 'assistant'}]