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: Medicine
[{'content': "Most important diagnostic sign of upper motor neuron\nsyndrome: \nSelect and explain. \nA. Exaggerated tendon reflexes, B. Babinski's sign -ve, C. Absent superficial reflexes, D. Lead pipe rigidity", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]