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
Ex-Press giaueoma implant is oiaily up of: 
Select and explain. 
A. Silicone, B. Titanium, C. Gold, D. Stainless steel
D: Stainless steel
Answer: D: Stainless steel 
Explanation: Ans. d. Stainless steel