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
Cataract is a cause of: 
Select and explain. 
A. Painful sudden vision loss, B. Painless sudden vision loss, C. Painful gradual vision loss, D. Painless gradual vision loss
D: Painless gradual vision loss
Answer: D: Painless gradual vision loss 
Explanation: Painless gradual vision loss