This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
Shape of tracheal cailage: 
Select and explain. 
A. W shaped, B. O shaped, C. C shaped, D. D shaped
C: C shaped
Answer: C: C shaped 
Explanation: Trachea is kept patent by the presence of U-shaped bars (rings) of hyaline cailage embedded in its wall. The posterior free ends of the cailage are connected by smooth muscle, the trachealis muscle.