<prompt> All of the following are true about antitussives, exceptDextromethorphan is a NMDA blocker which acts as central antitussiveAmbroxol is a mucolytic that causes depolymerisation of mucopolysaccharidesCarbocistene is a mucolytic with free sulphydryl groupBaclofen is a peripheral acting antitussive  <response>: Carbocistene contains blocked sulphydryl group. 