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
Anti-smoking drug is? 
Select and explain. 
A. Theophylline, B. Biclutamide, C. Salmeterol, D. Varenicline
D: Varenicline
Answer: D: Varenicline 
Explanation: Ans. (d) VareniclineRef Harrison 17/e, chapter 390