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: Surgery
[{'content': "When patient is asked to look down, his upper eyelid fails to follow the rotation of the eyeball and thus lags behind, this eye sign is known as: \nSelect and explain. \nA. Von Graffe's sign., B. Joffroy's sign., C. Moebius sign., D. Stellwag'sign.", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]