This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oral Cavity, Subject name: Surgery
[{'content': 'Structure preserved in Radical Neck Node dissection: \nSelect and explain. \nA. Vagus nerve, B. Spinal Accessory Nerve, C. Internal Jugular Vein, D. Sterno cleido mastoid muscle', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) Vagus nerve(Ref Sabiston 20th Edition Page 794)* Standard RND (CRILE operation) removes nodal levels I through V and the sternocleidomastoid muscle, internal jugular vein, cranial nerve XI, cervical plexus, and submandibular gland.* Modified RND (Bocca Operation) preserves one or more of the three structures - SCM, IJV and Spinal Accessory nerve.', 'role': 'assistant'}]