This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Autonomic nervous system, Subject name: Pharmacology
[{'content': 'What is Ecothiophate? \nSelect and explain. \nA. Directly acting cholinergic drug, B. Acetyl cholinesterase inhibitor, C. Anti cholinergic drug, D. Sympathomimetic', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Echothiophate is an OP compound which is an irreversible cholinesterase inhibitor Ref: KDT 6th ed pg 105', 'role': 'assistant'}]