This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Glaucoma, Subject name: Ophthalmology
Ex- Press glaucoma implant- 
Select and explain. 
A. Stainless steel, B. Gold, C. Silicone, D. Titanium
A: Stainless steel
Answer: A: Stainless steel 
Explanation: The EX-PRESS(r) Glaucoma Filtration Device is intended to reduce IOP in glaucoma patients when medication and conventional surgical treatments have failed. The device channels aqueous humor through a secure lumen (of either 50 mm or 200 mm) to a half-thickness scleral flap, creating a subconjunctival filtration bleb. This Lumenal Control means uniform filtration; uniform filtration helps to stabilize IOP during and after the procedure; and stable IOP means greater predictability.