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: Ophthalmology
[{'content': "Diameter of the Vossius's ring is: \nSelect and explain. \nA. Equal to normal pupil, B. Smaller than the normal pupil, C. Slightly larger than the normal pupil, D. Much larger than the normal pupil", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Smaller than the normal pupil', 'role': 'assistant'}]