This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Radiology
[{'content': 'Luftsichel sign on chest radiograph is indicative of \nSelect and explain. \nA. RUL collapse, B. Combined RLL and RML collapse, C. LUL collapse, D. LLL collapse', 'role': 'user'}, {'content': 'Answer: C \nExplanation: .', 'role': 'assistant'}]