This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Head and neck, Subject name: Anatomy
[{'content': 'Which one of the following structures is not enclosed by the carotid sheath? \nSelect and explain. \nA. Internal jugular vein, B. Carotid aery, C. Vagus nerve, D. Cervical sympathetic chain', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The cervical sympathetic chain lies behind the carotid sheath,plastered to the preveebral fascia. The contents of carotid sheath are common or internal carotid aeries,internal jugular vein and the vagus nerve. Notes:In the upper pa of sheath there are IX,XI,XII nerves also . These nerves pierce along with the external carotid aery. REF.BDC VOL.3,sixth edition pg 85', 'role': 'assistant'}]