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': 'Earliest symptom in corneal ulcer is: \nSelect and explain. \nA. Loss of sensation, B. Diminished vision, C. Photophobia, D. Pain', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. Pain', 'role': 'assistant'}]