This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CVS Embryology, Subject name: Anatomy
A 3-day-old boy delivered at 32 weeks of gestation is experiencing respiratory distress syndrome. The physician detects a hea murmur characteristic of a patent ductus aeriosus, a diagnosis that is confirmed with an echocardiogram. Which embryonic structure is involved in this diagnosis? 
Select and explain. 
A. Left third aoic arch, B. Right third aoic arch, C. Left sixth aoic arch, D. Umbilical aeries
C: Left sixth aoic arch
Answer: C: Left sixth aoic arch 
Explanation: C. Patent ductus aeriosus (PDA) is a condition in which the ductus aeriosus, a bloodvessel that allows blood to bypass the baby's lungs before bih, fails to normally close afterbih. The ductus aeriosus is derived from the distal poion of the left sixth aoic arch