This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parasympathetic System & Glaucoma, Subject name: Pharmacology
[{'content': 'Mechanism of action of oxybutynin is:- \nSelect and explain. \nA. Cholinergic muscarinic receptor agonist, B. Cholinergic muscarinic receptor antagonist, C. Cholinergic nicotinic receptor antagonist, D. Cholinergic nicotinic receptor agonist', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Oxybutynin is an anticholinergic drug used in overactive bladder. It acts by blocking M3 muscarinic receptors. It has maximum risk of causing dry mouth and other anti-cholinergic adverse effects.', 'role': 'assistant'}]