This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Retina, Subject name: Ophthalmology
Macular degeneration is caused by: 
Select and explain. 
A. Chronic alcoholism, B. Smoking, C. Diabetes mellitus, D. Eales disease
B: Smoking
Answer: B: Smoking 
Explanation: b smoking refkhurana 3rd/e p. 282