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
[{'content': 'All of the following are true about antitussives, except \nSelect and explain. \nA. 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', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Carbocistene contains blocked sulphydryl group.', 'role': 'assistant'}]