This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
[{'content': 'Varenicline is used in \nSelect and explain. \nA. Pulmonary hemosiderosis, B. Sleep apnea, C. Anti-trypsin deficiency, D. Nicotine dependency', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Varenicline is a prescription medication used to treat smoking addiction. This medication is the first approved nicotinic receptor paial agonist. Specifically, varenicline is a paial agonist of the alpha4/beta2 subtype of the nicotinic acetylcholine receptor Ref Davidson 23rd edition pg 578', 'role': 'assistant'}]