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': "Snellen's chart is based on \nSelect and explain. \nA. Light sense, B. Colour sense, C. Contrast sense, D. Form sense", 'role': 'user'}, {'content': "Answer: D \nExplanation: Snellen's chart is based on Form sense.", 'role': 'assistant'}]