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: Medicine
CSF glucose level is - 
Select and explain. 
A. Half the plasma glucose, B. 2/3 of plasma glucose, C. 1/3 of plasma glucose, D. Same as plasma glucose
B: 2/3 of plasma glucose
Answer: B: 2/3 of plasma glucose 
Explanation: None