This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory Radiology, Subject name: Radiology
[{'content': 'Flat waist sign is seen in \nSelect and explain. \nA. Right upper lobe collapse, B. Right middle lobe collapse, C. Left upper lobe collapse, D. Left lower lobe collapse', 'role': 'user'}, {'content': 'Answer: D \nExplanation: FLAT WAIST SIGN Flattening of the contours of the aoic knob and adjacent main pulmonary aery. Seen in left lower lobe collapse Caused by leftward displacement and rotation of the hea', 'role': 'assistant'}]