This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Radiology
[{'content': 'Dirty chest appearance on CXR is seen in? \nSelect and explain. \nA. Chronic bronchitis, B. TB, C. Bronchiectasis, D. Cystic fibrosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans ADirty chest appearance-because of recurrent infection with scarring, the bronchovascular structures have irregular contours. This is the only sign of bronchitis in chest X-ray.', 'role': 'assistant'}]