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': 'Posterior boundary of carotid triangle is - \nSelect and explain. \nA. Omohyoid superior belly, B. Sternocleidomastoid posterior margin, C. Digastric posterior belly, D. Sternocliedomastoid anterior margin', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Posterior boundry of carotid triangle is formed by anterior border of sternocleidomastoid.', 'role': 'assistant'}]