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: Surgery
[{'content': 'What is sternocleidomastoid tumor? \nSelect and explain. \nA. Hematoma of sternocleidomastoid muscle, B. Malignancy of sternocleidomastoid muscle, C. Lymphnodes related to the muscle, D. Benign tumor of the said muscle', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]