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': 'Drug of choice or differential blockade is \nSelect and explain. \nA. Lignocaine, B. Ropivacaine, C. Bupivacaine, D. Dibucaine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ropivacaine is pure S- isomer of bupivacaine,so less cardiotoxic than bupivacaine. It is drug of choice for differential block.', 'role': 'assistant'}]