This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Physiology
[{'content': 'Methoctramine is a \nSelect and explain. \nA. Selective M1 antagonist, B. Selective M2 antagonist, C. Selective M3 antagonist, D. Nonselective (M1+M2 ) agonist', 'role': 'user'}, {'content': 'Answer: B \nExplanation: .', 'role': 'assistant'}]