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: Pharmacology
Which of the following does not cross the blood brain barrier ? 
Select and explain. 
A. Pralidoxime, B. Obidoxime, C. Diacetyl monoxime, D. Physostigmine
A: Pralidoxime
Answer: A: Pralidoxime 
Explanation: None