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 is not an alkaloid ? 
Select and explain. 
A. Morphine, B. Neostigmine, C. Emetine, D. Atropine
B: Neostigmine
Answer: B: Neostigmine 
Explanation: None