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': 'Isthmus of thyroid gland is across tracheal rings: \nSelect and explain. \nA. 2nd - 4th, B. 3rd - 5th, C. 5th and 6th, D. 4th only', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The isthmus of the thyroid gland extends across the midline in front of the 2nd, 3rd, and 4th tracheal rings.', 'role': 'assistant'}]