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
Blood brain barrier is crossed by: a) Dopamine b) Propranolol c) Glycopyrrolate d) Physostigmine e) Streptomycin 
Select and explain. 
A. abcd, B. bcde, C. ad, D. bd
D: bd
Answer: D: bd 
Explanation: None