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: Radiology
Water lily appearance in chest X-ray suggestive of: 
Select and explain. 
A. Bronchiectasis, B. Bronchopleural fistula, C. Hydatid cyst, D. Sequestration cyst of lung
C: Hydatid cyst
Answer: C: Hydatid cyst 
Explanation: Hydatid cyst is caused by the parasite echinococcus granulosus. It is often associated with hydatid cyst of liver.It is usually single buy multiple hydatis cysts can occur. In chest X-ray a dense homogenous opacity can be seen. A collapsed laminated membrane produces an irregular projections in a fluid level due to rupture of the cyst which shows a characteristic 'water lily' appearance on chest X-ray. Ref : Tsung A. (2010). Chapter 31. Liver. In T.R. Billiar, D.L. Dunn (Eds), Schwaz's Principles of Surgery, 9e.