This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
Which of the following is not permeable through the Blood Brain Barrier 
Select and explain. 
A. Water, B. Lipophilic drugs, C. Gas, D. Proteins
D: Proteins
Answer: D: Proteins 
Explanation: Ans. (d) Proteins(Ref: Ganong, 25th ed/p. 607)Substances that crosses the Blood Brain Barrier easily are,#Water (using carrier protein Aquaporin -4)#Glucose (using glucose transporters GLUT 1 55K and GLUT 1 45K)#O2 #CO2 #Steroid hormonesSubstances that do not crosses the Blood Brain Barrier easily are,#Protein hormones#Dopamine#H+ ions#Bicarbonate ions