This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Intravenous Anesthetic Agents, Subject name: Anaesthesia
[{'content': 'Which intravenous anaesthetic can be used for upper airway manipulation in absence of neuromuscular blockers- \nSelect and explain. \nA. Thiopentone, B. Propofol, C. Etomidate, D. Ketamine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Propofol - induced depression of upper airway reflexes exceeds that of any other agent thus allowing intubation, endoscopy or laryngeal mark placement in absence of neuromuscular blockers. ketamine preserve upper airway reflexes.', 'role': 'assistant'}]