This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardio thoracic surgery  , Subject name: Surgery
[{'content': 'All of the following statements regarding branchial cysts are true except \nSelect and explain. \nA. Seen in mediastinum, B. 50-70% occur in lung, C. Are commonly infected, D. Multilocular', 'role': 'user'}, {'content': "Answer: B \nExplanation: .BRANCHIAL CYST It arises from the remnants of second branchial cleft. Normally 2nd, 3rd, 4th clefts disappear to form a smooth neck. Persistent 2nd cleft is called as cervical sinus which eventually gets sequestered to form branchial cyst. Features * Swelling in the neck beneath the anterior border of upper third of the sternomastoid muscle. It is smooth, soft, fluctuant, often transilluminant with a sensation of 'Half-filled double hot water bottle'. ref:SRB&;s manual of surgery,ed 3,pg no 381", 'role': 'assistant'}]