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
[{'content': 'Shape of tracheal cailage: \nSelect and explain. \nA. W shaped, B. O shaped, C. C shaped, D. D shaped', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 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.', 'role': 'assistant'}]