This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Substance Related and Addictive Disorders, Subject name: Psychiatry
[{'content': 'The main metabolite of nicotine is \nSelect and explain. \nA. Nornicotine, B. Carboxynicotine, C. Cotinine, D. Nicotine hydroxide', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Nicotine is metabolized in liver, lung and brain to cotinine by CYP2A6 enzyme. A plasma cotinine levels of >14ng/ml typically indicates smoking.', 'role': 'assistant'}]