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 true about antitussives, except 
Select and explain. 
A. Dextromethorphan is a NMDA blocker which acts as central antitussive, B. Ambroxol is a mucolytic that causes depolymerisation of mucopolysaccharides, C. Carbocistene is a mucolytic with free sulphydryl group, D. Baclofen is a peripheral acting antitussive
C: Carbocistene is a mucolytic with free sulphydryl group
Answer: C: Carbocistene is a mucolytic with free sulphydryl group 
Explanation: Carbocistene contains blocked sulphydryl group.