This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anatomy
[{'content': 'What is the power of the lens used to view retina with this instrument? \nSelect and explain. \nA. +20D, B. +30D, C. +15D, D. +90D', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Indirect ophthalmoscopy needs usage of +20 D', 'role': 'assistant'}]