<prompt> The respiratory syncytial virusThe respiratory syncytial virusThe para influenza virusThe adenovirusThe coronavirus  <response>: Croup tLarvngotracheobronchitiso Croup is a viral infection of upper respiratory tract,o Children between the age of 1-5 years are affected,o Para-influenza type I virus is the most common causative organism.o Other viruses implicated in causaction are RSV, influenza virus, Adneovirus and Rhinovirus. 