This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pharmacology
[{'content': 'In the hea, which muscarinic receptor inhibits adenyl cyclase activity? \nSelect and explain. \nA. M1, B. M2, C. M3, D. M4', 'role': 'user'}, {'content': 'Answer: B \nExplanation: M2 receptors are located in the hea.Ref: HL Sharma 3rd ed Pg: 119', 'role': 'assistant'}]