This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and Errors of Refraction, Subject name: Ophthalmology
[{'content': 'Resolution when visual acuity is 6/6: \nSelect and explain. \nA. 1 minute of an arc, B. 5 minutes of an arc, C. 6 minutes of an arc, D. 10 minutes of an arc', 'role': 'user'}, {'content': "Answer: A \nExplanation: Resolution when visual acuity is 6/6 is 1 minute of an arc. Snellen's test types: The distant central visual acuity is usually tested by Snellen's test types. The fact that two distant points can be visible as separate only when they subtend an angle of 1 minute at the nodal point of the eye, forms the basis of Snellen's test-types. The lines comprising the letters have such a breadth that they will subtend an angle of 1 min at the nodal point. The entire character (optotype) subtends an angle of 5 min of an arc at the nodal point, each stroke is 1 min at the nodal point.", 'role': 'assistant'}]