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: Pediatrics
A recognised cause of stridor in newborn – 
Select and explain. 
A. Cystic hygroma, B. A Vascular ring, C. Laryngomalacia, D. All are true
D: All are true
Answer: D: All are true 
Explanation: Stridor

Stridor refers to the physical finding of excessively noisy breathing and is generally due to airway obstruction.

Causes of Stridor in a child.
Infections

Croup (laryngotracheobronchitis)
Epiglottitis
Bacterial tracheitis
Retropharyngeal abscess

Congenital

Laryngomalacia
Vocal cord palsy
Subglottic stenosis
Vascular ring
Saccular cyst

Neoplasms

Subglottic hemangioma
Laryngeal papillomas
Cystic hygroma, when it occurs in larynx then it can cause respiratory tract obstruction - Nelson 18th/ep. 1773