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': 'Swelling situated in the posterior triangle of the neck \nSelect and explain. \nA. Cystic hygroma., B. Branchiogenic carcinoma., C. Collar stud abscess., D. All of the above.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]