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 macula lutea is: \nSelect and explain. \nA. 1.5 mm, B. 3.5 mm, C. 4.5 mm, D. 5.5 mm', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. 5.5 mm', 'role': 'assistant'}]