This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thorax, Subject name: Anatomy
Structures at Angle of Louis 
Select and explain. 
A. Arch of aoa, B. Azygous vein, C. Common carotid aery, D. Clavicle
A: Arch of aoa
Answer: A: Arch of aoa 
Explanation: Sternal angle/Louis angle:It is felt as a transverse ridge about 5cm below the suprasternal notch.It marks the manubriosternal joint and lies at the level of the second costal cailage anteriorly and the disc between the fouh and fifth thoracic veebrae posteriorly.This is an impoant landmark for many reasons.The arch of aoa begins and also ends at this level. BD CHAURASIA'S HUMAN ANATOMY UPPER LIMB THORAX SIXTH EDITION VOLUME 1.PAGE NO187