This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Pharmacology
[{'content': 'Drug used for cessation of smoking - \nSelect and explain. \nA. Theophylline, B. Biclutamide, C. Salmeterol, D. Varenicline', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., Varenicline o Varenicilline is a direct acting nicotine agonist with selective action on a4 b2 isoform of Nm receptors. It is an antismoking drug.", 'role': 'assistant'}]