This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
[{'content': 'All except one can cross blood brain barrier \nSelect and explain. \nA. Neostigmine, B. Atropine, C. Lignocaine, D. Physostigmine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Neostigmine being quaternary amine , is highly ionised and does not cross blood brain barrier.', 'role': 'assistant'}]