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
A 5-year-old boy had been playing with his little race cars. Soon after he put a wheel from one of the cars in his mouth, he began choking and coughing. Where in the tracheobronchial tree is the most common site for a foreign object to lodge? 
Select and explain. 
A. The right primary bronchus, B. The left primary bronchus, C. The carina of the trachea, D. The beginning of the trachea
A: The right primary bronchus
Answer: A: The right primary bronchus 
Explanation: The right main bronchus is the shorter, wider, and more vertical primary bronchus. Therefore, this is most often the location that foreign objects will likely be lodged. The left primary bronchus is not as vertical and therefore does not present the path of least resistance. (It must be understood, however, that in some cases of aspiration, the foreign body can pass into the left primary bronchus rather than the right bronchus!) The carina is a ridge separating the openings of left and right bronchi, the "fork in the road," so to speak. The trachea is a tubular structure supported by incomplete cartilaginous rings, and the likelihood that an object will be lodged there is minimal. It is unlikely that a foreign object would descend so far as to obstruct a tertiary bronchus, although this could happen.