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': "The principle of the stenopaeic slit test is based on: \nSelect and explain. \nA. Astigmatic fan, B. The circle of least diffusion, C. Pin-hole phenomenon, D. Sturm's conoid", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Pin-hole phenomenon', 'role': 'assistant'}]