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 of the following are expectorants except 
Select and explain. 
A. Hypertonic saline, B. Guaifenesin, C. Ammonium chloride, D. Noscapine
D: Noscapine
Answer: D: Noscapine 
Explanation: Noscapine is a central acting antitussive, which is an opioid agonist.