This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nose and paranasal sinuses, Subject name: ENT
Most common cause of U/L mucopurulent rhinorrhea in a child is: 
Select and explain. 
A. Foreign body, B. Adenoids which are blocking the airways, C. Deted nasal septum, D. Inadequately treated acute frontal sinusitis
A: Foreign body
Answer: A: Foreign body 
Explanation: A unilateral nasal discharge is nearly always due to foreign body and if duscharge has an unpleasant smell,it is pathognic. If a child presents with unilateral,foul smeling nasal discharge,foreign body must be excluded. Ref Dhingra 6/e,p 161.