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
All these drugs EXCEPT one cross the blood–brain barrier: 
Select and explain. 
A. Morphine, B. Dopamine, C. Propranolol, D. Ether
B: Dopamine
Answer: B: Dopamine 
Explanation: None