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: Pharmacology
[{'content': 'An agent added to local anaesthetics to speed the onset of action is : \nSelect and explain. \nA. Methylparaben, B. Bicarbonate, C. Fentanyl, D. Adrenaline', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]