This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular Radiology, Subject name: Radiology
Angle of tracheal bifurcation is increased in which chamber of hea enlargement. 
Select and explain. 
A. Left atrium, B. Right atrium, C. Left ventricle, D. Right ventricle
A: Left atrium
Answer: A: Left atrium 
Explanation: Normal tracheal angle: 40- 80deg The angle of tracheal bifurcation may be widened in the following conditions due to the mechanical splaying of the bronchi: Subcarinal masses Lobar collapse Left atrial enlargement Generalized cardiomegaly Pericardial effusion