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
Sandstorm appearance on Chest radiograph is characteristic of? 
Select and explain. 
A. Pulmonary edema, B. Pulmonary alveolar proteinosis, C. Pulmonary alveolar microlithiasis, D. Pulmonary thromboembolism
C: Pulmonary alveolar microlithiasis
Answer: C: Pulmonary alveolar microlithiasis 
Explanation: Pulmonary alveolar microlithiasis is a chronic disease characterized by widespread diffuse bilateral intraalveolar accumulation of minute calculi (microlithiasis) especially in mid and lower zones, giving characteristic sandstrom appearance on chest radiographs.