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': 'Ex-Press giaueoma implant is oiaily up of: \nSelect and explain. \nA. Silicone, B. Titanium, C. Gold, D. Stainless steel', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. d. Stainless steel', 'role': 'assistant'}]