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: Pathology
[{'content': 'The most common cause of SVC syndrome is - \nSelect and explain. \nA. Thrombosis, B. Extrinsic compression, C. Mediastinal lymphoma, D. Teratoma', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]