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
Commonest cause of loss of vision in non-proliferative diabetic retinopathy is: 
Select and explain. 
A. Vitreous haemorrhage, B. Macular edema, C. Detachment of retina, D. Subretinal haemorrhage
B: Macular edema
Answer: B: Macular edema 
Explanation: Ans. Macular edema