Vascular ring

Q  ) Which is a true vascular ring?

a) Pulmonary artery sling

b) Double aortic arch

c) Cervical aortic arch

d) Origin of subclavian artery from descending aorta

30 ) b 
Double aortic arch is a true (complete) vascular ring where they encircle and may
constrict the trachea and esophagus. Aberrant origin of Rt. SCA from descending
aorta is a partial vascular ring, cervical aortic arch is an aortic arch anomaly
characterized by elongated, high lying aortic arch and is not a vascular ring.