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
Facility of aqueous outflow is ______I/min/mm Hg. – 
Select and explain. 
A. 0.8, B. 0.6, C. 0.4, D. 0.2
D: 0.2
Answer: D: 0.2 
Explanation: The average C-value (facility of aqueous outflow) is 0.28 ± 0.05 1/min/mmHg.