<prompt> A child with three days history of upper respirotory tract infection presents with stridor, which decreases on lying down postion. What is the most probable diagnosisAcute EpiglottitisLaryngotracheobronchitisForeign body aspirationRetropharyngeal abscess  <response>: Biphasic stridor usually originates from subglottic or proximal tracheal lesions. laryngotracheobranchitis presents in children of 1-5 years of age with biphasic stridor,brassy coughlow grade fever. Ref : Essential Paediatrics,O.P.Ghai,7 th edition,Pg No:339 