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
Mechanism of action of oxybutynin is:- 
Select and explain. 
A. Cholinergic muscarinic receptor agonist, B. Cholinergic muscarinic receptor antagonist, C. Cholinergic nicotinic receptor antagonist, D. Cholinergic nicotinic receptor agonist
B: Cholinergic muscarinic receptor antagonist
Answer: B: Cholinergic muscarinic receptor antagonist 
Explanation: 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.