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': 'Objective of ETDRS study is \nSelect and explain. \nA. Effect of aspirin on the course of diabetic retinopathy, B. To observe patients with severe DR in type 1 and type 2 diabetes over 2 years to determine visual outcomes, C. To evaluate whether photocagulation prevents severe visual loss in eyes with diabetic retinopathy, D. ALL of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Option A - ETDRS study\nOption C\xa0- DRS study\nOption B - DRVS study', 'role': 'assistant'}]