This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Integrated QBank, Subject name: Unknown
A 37-day-old baby presented to the Pediatrics ER with increased respiratory effo along with grunting. Mother says he is always irritable, feeds very poorly and has not gained weight. History of frequent respiratory infections in the past 2 weeks O/E, Wide pulse pressure along with bounding peripheral pulses Hyperkinetic apex Continuous murmur in 2nd left intercostal space. The structure involved in the above condition develops from which embryological structure: - 
Select and explain. 
A. Left sixth arch, B. Right sixth arch, C. Left fifth arch, D. Right fifth arch
A: Left sixth arch
Answer: A: Left sixth arch 
Explanation: Chest x-ray shows marked cardiomegaly with dilatation of the main pulmonary aery and bilateral pulmonary plethora ECG tells la dilatation, LV hyperophy and left axis detion which points towards the diagnosis of PDA. The left sixth aoic arch is responsible for the development of both the pulmonary aeries and the ductus aeriosus. Without regression of the ductus aeriosus, a patent connection remains between aoa and the pulmonary trunk. The ductus aeriosus often reaches functional closure within 24 hours after bih, whereas anatomic closure and subsequent formation of the ligamentum aeriosum often occur by the twelfth postnatal week.