The exam is a comprehensive question, which should have been more difficult, but the candidates did well in the exam, probably because they were impressed with the correct answer. This question requires candidates to fully grasp the systematic anatomy and local anatomy of trachea. The trachea is in front of the esophagus, excluding alternative answers.

a； The upper end of trachea is connected with cricoid cartilage, which excludes alternative answers.

b； The cartilaginous ring of trachea is "C" shaped rather than annular, and the alternative answer C is excluded; Tracheotomy is mostly performed at the 2 nd to 4 th tracheal cartilaginous rings, and the alternative answer e is excluded, so the correct answer is D.