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
The commonest cause of rubeosis iridis is 
Select and explain. 
A. Diabetes mellitus, B. Central retinal vein occlusion, C. Central retinal aery occlusion, D. Carotid stenosis
A: Diabetes mellitus
Answer: A: Diabetes mellitus 
Explanation: Ans. Diabetes mellitus