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: Physiology
Neutral substance which have size of 6 nm are 
Select and explain. 
A. Freely filtered, B. Permeability is inversely proportional to diameter, C. Not filtered, D. None of the above
B: Permeability is inversely proportional to diameter
Answer: B: Permeability is inversely proportional to diameter 
Explanation: Neutral substances
< 4nm ⇒ freely filtered
> 8mm ⇒ not filtered
4nm - 8nm ⇒ Permeability is inversely proportional to diameter