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 the thyroid gland is across tracheal ring - \nSelect and explain. \nA. 2nd to fourth, B. 3rd to fifth, C. 5th and 6th, D. 4th only', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The isthmus extends from the second to the fourth tracheal ring.', 'role': 'assistant'}]